This condition reflects a creature's disposition toward a particular character, and only supernatural effects (like a spell) can impose this condition on a PC.
A creature that is Friendly to a character likes that character. They are likely to agree to requests from that character as long as they are simple, safe, and don't cost too much to fulfill.
If the character (or one of their allies) uses a Hostile action against the creature, the creature gains a worse attitude condition depending on the severity of the Hostile action, as determined by the GM.