Searching the forums would be a good place to start...
But very generally speaking, mixing is MIXING together all the elements of the mix while tailoring those individual elements to best serve the mix. Yes, that includes effects, spatial, modulatory, equalization, dynamics and volume manipulation, etc.
Mastering is the creation of the production MASTER - Taking (typically a collection of) finished mixes and preparing them for replication or distribution by tailoring individual mixes to best serve the finished master. Still involving equalization, volume & dynamics manipulation, but with a different purpose across elements.
That's about as general as a definition as it gets. I could go on for hours on what actually happens during mastering vs. what some think happens during mastering vs. the goals of the mixing vs. mastering engineer (which are many times at odds with each other), but that's really probably a search function thing...