This is very true.
A couple weeks of steady research even on this site will do you good, but here's a quick terminology lesson:
When you are in the process of putting tracks down, you are tracking; when you are sitting there editing tracks, changing things like pan and volume on different channels, etc., you are mixing.
When you have finished your multi-track mix and are converting it to a stereo/mono/quadraphonic/5.1/7.1/yada yada mix, you are creating a mixdown, final version of the song.
When you take that final mix (in stereo/mono/etc format), and make overall changes, such as applying compression, perhaps some EQ, some overall volume changes to make it match up better with the other songs for your album/getting it closer to the "norm", you are mastering.
This is a very basic description, you should use the search function to read up on the various concepts. As for which is a decent interface, I checked that link, it goes to a decent thread that should help out. What kind of mics do you have at the moment, and are you planning on upgrading those as well?