Depends what camera you are talking about
Some bodies are weather shielded - but you'd have to look it up really. Stuff like rubber around / inside where the buttons are. rubber around the flash card cover. Lenses depend again on what lens it is. I used one at the weekend in the rain which afaik wasn't water tight, but it was OK. the camera body was water tight tho so I didn't care about that.
Usually I try and give it a nice toweling and maybe some car aircon to dry it out after.
The camera above loves the rain though - came out nice and clean too!