OH LORD. so you dont know anything about AC. my advice is that if your good with tools and know how to work on cars, you can do this job but to PROPERLY do this you need about $300 in tools that you dont have. in a very VERY nut shell of a explanation. you need to do many things in the right order and replace and clean the right parts with proper ones and not be stingy with them. you need a REAL set of gauges not the ones from autozone on the can a vacuum pump, PAG oil, leak tester, cans of 134a (NO ADDITIVES) and lots of time and a warm garage to do this in or you need to calculate your supper cool supper heat values for cold weather.
my advice, pay someone $$$ to do the job. You can but the parts if you want, but you need to CLEAN and purge the parts you get from the junk yard 100% with the right chemicals. if your interested in taking this project on, take it from me, i used to do HVAC for 3 years and now i do it on the side. You can go elcheep'o now and just slam part on it, vac it down and dump some bs can from autozone in it but you will have just destroyed your system in less than 1 years time of use.
AC is only done one way, the right way. any other way is wrong.
Technically you need to hook up a recovery tank and pump to whatever parts you are taking off, its a federal law that you broke but you will be ok, we wont tell!