Sometimes I get a message to be sure to vote, but I can't seem to find a place to do it. Some answers are just great, and I'd like to give them a positive rating. Please tell me how to do this.
You should see arrows around the post score (to the left over every post). You can see an example at https://stackoverflow.com/about.
If you don't see them, we'll need some extra information like your browser and operating system, and what posts you'd like to vote on. (As Asad mentioned, some are locked and voting is disabled on them.)