It is mentioned in Garuda Purana that if one doesn't begets a couple does not begets a son in their lifetime and the line is broken, they have to spend a certain time in a hell named Put. However I am not able to find any descriptions of this hell. In which scripture, does it describe this hell ?
There is no hell mentioned in any major canonical text, which goes by the name of 'Put' or 'Puṃ'.
This hell doesn't exist, as a specific place like Mahāraurava or Kumbhīpāka, etc. The word is more of an 'attributive adjective declaration' of the condition a parent is forced to undergo (especially in their old age) if they lack a progeny. 'Put' is a metaphorical/esoteric signifier of hell-like sufferings.
The mention of a hell named - Pum (पुम्) or Put (पुत्) or Pud (पुद्) or Pun (पुन्), occurs in puranas, the Mahabharata (Chapter CXXIV, Ādi Parva) and Manusmṛti 9.138 too.
We get our answer from Manusmṛti in reference with Medhātithi’s Manubhāṣya:
पुन्नाम्नो नरकाद् यस्मात् त्रायते पितरं सुतः ।
तस्मात् पुत्र इति प्रोक्तः स्वयमेव स्वयम्भुवा ॥ १३८ ॥
- Because the Son delivers his father from the hell called ‘Put,’ therefore has he been called ‘Putra,’ ‘Deliverer from Put,’ as ordained by the Self-existent One Himself.
On first reading, this does sound like a specific hell. However, the commentary by Ācārya Medhātithi makes it clear, that it's not so:-
Medhātithi’s commentary (manubhāṣya):
तनस्वायते पुत्रोजातः देवयोनौ जातइत्यर्थः तस्माद्धेतोः पुत्रइति व्यपदिश्यते ॥
This is a declamatory supplement to the Injunction of begetting children.
‘The hell called Put’—is the name given to the four kinds of elemental life on the Earth. And from this is the father delivered by his son, as soon as he is born; which means that he is born next in a divine life.
It is for this reason that he is called ‘Putra,’ ‘Deliverer from Put.’—(138)
English Translation by Ganganatha Jha
Dr. Surendra Kumar explains this as follows:
(यः) जो (सुतः) पुत्र (पितरम्) माता-पिता को (पुम् नाम्नः नरकात्) "पूम् =वृद्धावस्था आदि से उत्पन्न होने वाले दुःखों से (त्रायते) रक्षा करता है" (तस्मात्) इस कारण से (स्वयंभुवा स्वयमेव "पुत्रः" इति प्रोक्तः) स्वयंभू ईश्वर ने वेदों में बेटे की पूत्र'संज्ञा से अभिहित किया है ॥
So, basically, 'Pum' here signifies the problems/sufferings that arise with old age, which is equated with a horrible experience, similar to hell (narak).