nasloniti

1. (na + acc.) to lean; to rest
   Naslonio je bicikl na zid i ušao u prodavnicu. — He leaned the bike against the wall and went into the shop.
   Naslonila je glavu na moje rame. — She rested her head on my shoulder.
2. (nasloniti se na + acc.) to lean against; to lean back
   Naslonio se na ogradu i zapalio cigaretu. — He leaned on the railing and lit a cigarette.
   Nasloni se i opusti, vožnja je duga. — Lean back and relax, it's a long ride.

For the figurative "rely on someone", osloniti se na is usually used instead.