Do these things exist anywhere in Hindu scriptures (Vedas, upnishads, Geeta etc.)?
Or are they later created by Brahmins?
All the things you have asked has been mentioned in the scriptures. Krishna Yajurveda mentions the names of various kind of Vedic Yajnas and the fruits that are obtained upon their performance.
Smritis also elaborate how to perform some the basic Yajnas alongwith giving the appropriate ingredients and mantras.
.... (sacrifices) with the help of the Avasathya fire (the sacred fire kept in the house). He, whose A'vasathya fire has not been lighted at all, should perform the Homa by casting oblations of boiled rice soaked in clarified butter in the Laukika fire, according the regulations of the Sakala (a school of the Rig- Veda) school. (27 28)
The oblations should be cast in the sacred fire by severally and combinedly reciting the Vyahritis and the six Mantras running as Deva Kritasya etc., (29)
After that, the Prajapatya Svishta Krita Homa should be performed by offering twelve oblations unto the fire, prefixing Om and appending Svaha to the Mantra according to the Svishta regulation. (30)
The oblations should be offered on Kusha blades spread out on the ground ; and the one, well-versed in the S'astras should first offer three oblations by prefixing Om and appending Namas to the Mantra as follows : Om, to Vishvadevas (Namas) obeisance ; Om, to all the beings (Bhutas) Namas (obeisance); Om, to the lord of all the beings (Butanam Patayae) Namas (obeisance) ; and after that, Om, to Pitris (obeisance) Namas. (31 32)
Vyasa Smriti's Chapter 3
Wearing the sacred thread over the right shoulder and under the left arm, one should perform the tarpana for the Pitris and the Vis'wadevas. Then when serving meals to the Deities, he should lower down his right knee. (41)
Then reciting, Somaya Pitrimate Swadha, namas, Agnaye Kavyavahanaya Swadha, he should offer oblations. (42)
Being self-restrained and stationed near the image of a Great Deity or in a cowpen, he should consign them to the hands of a Vipra in the absence of the Fire. (43)
Therefore having circumambulated, at the command [of the Brahmanas the [image of the] Deity and his own tutelary Deity, he should paint, with cowdung, before him, towards the south, on a little elevated place, an auspicious circular or square figure. He should, then, with a Kusa-reed, rub thrice inside the figure. (44 45)
Usana Smriti, Chapter 5
This is fire worship - the Vedic mode of worship. Now, we also have the Puranic and Tantric modes, where we do the worship in idols and Yantras, after invoking life-force in them with the help of mudras and mantras. The Tantric method recommends worship in Yantras.
Yantram mantramayam proktam devatA mantrarupini |
Yantre sA pujitA devi sahsaiva prasidAti ||
O Devi, know the Yantra to be Mantra-mayam (mantra-endowed) and the Deity to be of the form of mantra. If worshipped in Yantra, the deity is appeased instantly.
KulArnava Tantram 6.86
KAma-krodhAdi-doshattha sarva-dukkha-niyantranAt |
YantramityAhure-tasmin devah prinAti pujitah ||
Because it controls (or subdues) all the miseries arising from Kama (desire), Krodha (anger) etc it is called Yantra. If worshipped in a Yantra the deity is pleased.
KulArnava Tantram 6.87
And, the Purans also describe how to perform deity worship in an image or even in a Yantra.
From Devi Bhagavata Purana we have:
18-20. O king! When the ceremony has been thus commenced, one should place on the Vedî (a raised platform; an altar), the throne fitted with double silken clothes; and, on that throne, he should place the image of the Devî. The Devî, the Eternal World-Mother, is to be four-armed or eighteen armed, (4 or 18) fully provided with all the weapons, ornamented with garlands of pearls and jewels, decorated with various ornaments of gems and precious stones, wearing excellent heavenly clothings, all the parts of the image being artistically finished and endowed with all the auspicious signs, mounted on a lion, and holding conch shell, wheel, club, and lotus in Her hands. Note :-- The Devî, here, is represented with four (4) or eighteen (18) hands. 21-22. In the absence of the image, one should place an earthen water-pot, on that throne, thoroughly purified by the Vedîc Mantras, filled with gold and jewels, and filled fully with the water, brought from a sacred river or a sacred place of pilgrimage and with five young shoots of plants, the extremities of branches bearing new leaves immersed in water. Beside the water-pot on the throne, there should be a symbol (Diagram or Yantra) with the nine lettered Mantram (Om Hrîm S’rîm Chandikâyai namah) in it for the purpose of worship. 23. One should place on one’s side all the materials of worship in their due places, and then have the music and other sounding drums played, for the good fortune and prosperity of the family
Next, on an auspicious copper plate, he is to draw inside a six-angled (hexagonal) figure (two triangles crossing each other with their vertices one upward and the other below) with white sandal paste or with eight perfumed things and outside this figure, an octagonal figure of eight petals; outside this he is to draw the boundary lines that is called the Bhûpura. On each of the eight petals he is to write each letter of the nine-lettered Vîja (Seed) Mantram and the ninth letter in the central ovum. Next by the Mantram by which breath is infused or by the Vedic Mantram he will have to place the Yantra in the proper position and then worship the Âdhâra S’akti (the vital Force) in the central ovum and the holy seat with the Pîtha Mantrams. He will have to invoke the Devî, uttering the Seed Mantram over a golden plate or figure and carefully worship Her by offering seats and other articles duly as enunciated in the Yâmala Tântras, etc. Then he will have to perform the six-fold worship of the Ganas in the six angles and worship Indra, etc., and Vajra and others in the Bhûpura (the boundary) and thus finish the Poojâ of the Yantra.
Book 5, Chapter 34
The various offering that we make like Dhupa (incense), Deepa (lighted lamp) etc are also mentioned in Tantras and Puranas.
One should next present fourteen things, uttering proper mantras according to the Vedas. Then one must perform special pûjâ and chant hymns to the Devî and worship Her. The fourteen articles of worship are as under :-- (1) Seat (Âsan); (2) water for washing feet (Pâdya), (3) offering of rice and Durba grass (Arghya), (4) water for bath (Snânîya), (6) anointment with sandalpaste and other scents (Anulepana), (7) incense (Dhûpa), (8) Lights (Dipa), (9) offerings of food (Naivedya), (10) Betels (Tambûl), (11) Cool water, (12) garments, (13) ornaments, (14) garlands, scents, offering of water to sip, and beautiful bedding. While offering these articles, one is to utter the mantras, this beautiful wooden or golden seat, giving spiritual merits is being offered by me to Thee. This water from the Tîrthas, this holy water for washing Thy feet, pleasant, highly meritorious, pure, and as an embodiment of Pûjâ is being offered by me to Thee
Book 9, Chapter 26