Explaining all the aspects of performing these two jobs is not easily done here . Your best approach to working on your own vehicle is to purchase a good quality repair manual and thoroughly read up on the repair instructions. When it comes to diagnosing problems (like the A/C not working), then you really need to understand how that particular system works. So read up on automotive theory and then read the repair instructions, get the proper tools and safety equipment, then have a go at it.
I can tell you that I've seen many people tow their vehicle in to where I've worked with problems they've created because they get into repairs without doing their homework. They end up paying thousands of dollars because they tried to save a couple hundred dollars. Don't be this person!
I would get an online subscription to alldatadiy.com or chiltondiy.com, these online repair manuals are often exactly what the manufacturer gives to the Dealership Technicians, so the info is very good. They also include automotive theory.
Once you have done some research and are ready to perform the job, then ask any questions you have remaining.