Getting “their”, “they’re”, and "there"; “you’re” and “your”; "to", "too", and "two" mixed up might possibly be the sickest thing on earth. Literally.
If you don't know how to use these words correctly, don't use them. You look stupid and it annoys the hell out of me.
I'm pretty sure we learned the meanings and proper uses of these words by the time we were in second grade. Need a refresher? Check out these worksheets; if you have questions, do ask.