Does Hinduism say anything about ghosts? Like why they may be stuck here, if it's really the jiva or something else like it?
Yes, Hinduism says many things about ghosts. The Garuda Purana has good descriptions about it of which some are as below to answer your question:
When a person dies then he becomes a preta (Ghost). Generally this phase is temporary and as soon as the funeral rites are over, the preta state is over and the jiva then gets the status of Pitru (manes or forefathers). However, if the funeral rites are not duly performed or the death and actions of the person is not good then he may get stuck in the limbo or preta phase:
pāpakarmaratā ye vai pūrvakarmavaśānugāḥ
jāyante te mṛtāḥ pretāstāñchṛṇuṣva vadāmyaham [GP - 2.22.3]
He who is indulged in sinful activities goes to become a preta after death; that I am telling you please listen.
svaiḥ svaistu karmabhiḥ prāptaṃ pretatvaṃ hi dvijottama
paradroharatāḥ sarve pāpamṛtyuvaśaṃ gatāḥ [GP - 2.22.33]
O best among the twice-borns (dvijottama), one certainly attains the state of preta due to ones own actions. All those who are engaged in offence or enmity (droha) toward others, under the influence of sin and death go on to be come ghosts.
That chapter then describes many such activities doing which one goes into the preta state for certain. Basically if one commits sins, kills other, causes pain to elders, brother, sister etc. without any reason, who has forsaken rememberance of Vishnu, who doesn't perform fire sacrifices, etc. obtains the state of pretatva (ghost hood).