Deity worship 𖤐(*°∀°)=3

Why do people work with deities? Is there something to gain from it? I know the basics about deity worship but I haven't been able to find the answer to this question and I try to avoid using websites like Wikipedia because they can be untrustworthy with topics like this and none of the books I have cover it. 

Also how do you know a deity is calling out to you? Surely it's difficult to differentiate an actual sign and just something that happened to happen right place right time. I know you can use tarot cards but I don't see how they could be used to find out.