Che references all nouns, personal pronouns, demonstrative pronouns and some indefinite pronouns. It can be used in the relative clause as a nominative or accusative. Let's see some example.
1) Che references nouns
La casa che i miei genitori hanno costruito è bella.
The house which my parents has built, is nice.
2) Che references personal pronouns and indefinite pronouns
Lui che non ne sapeva niente, voleva spiegarlo agli altri.
He, who had no clue of that, wanted to explain it to the others.
Qualcuno che non conosco, voleva parlare con te.
Someone (that) I knew wanted to talk to you.
3) Che can be nominative as well as accusative
nominative in the relative clause : L' uomo che attraversa la strada è un amico mio.
=>The man who crosses the street is a friend of mine.
accusative in the relative clause : L' uomo che ho visto ieri, oggi ha parlato con me.
=> The man (that / who) I saw yesterday, has talked to me today.
If you speak French, you have a problem here. In French qui is subject, que accusative. This distinction doesn' t exist in Italian, it works like in Spanish. (More accurate: You can use chi, if the relative pronoun is the nominative of the relative clause, but it is not compulsory.)