Could someone please walk me through exactly what to do? Explain to me as if I have no clue...because I don't. haha.

Please tell me also if I will need to take my fish out to do this.

I have 1 diamond tetra, 2 cherry barbs, 1 red-tailed black shark, and a mystery fish who enjoys playing with my tetra, Dee.

When do you think would be a good time to put 2-3 more tetras, 1-2 more barbs? I believe I have somewhere between a 25-35 gallon tank.

I have some live plants I would like to put in. When should I do that? After cycling?

Any help would be really appreciated. This is a new hobby for me. I never thought I would so serious about fish, but them being living creatures, however "pointless" they seem, I want to do right by them. I have said fish were "pointless" but I really don't believe them to be anymore. They have won me over.

Here is a good link on how to cycle: http://www.kokosgoldfish.com/cycle.html

The first thing you need is a test kit because you will be testing the water for ammonia, nitrate, and nitrites pretty much every day. You can put plants in during a cycle

Is the cycling process the same if you have tropical fish in the tank during cycling?

Yep

When I cycle my tank, I have been keeping a few guppies (last time I kept a fancy guppy, but with my 10 gallon I bought 6 common guppies). I only test my water when I cycle once a week, sometimes twice a week if I see the ammonia working it's way up.

Since you have fish in the tank, make sure the Ammonia doesn't go up over 1 ppm. If it gets that high, change some of the water for a few days to help keep it from becoming to lethal for the fishies!

How long have you had the tank set up with fish in it? You may already be reaching toxic levels of ammonia. You need a test kit! If you can't get one right away, you should start doing regular water changes (10-20%) daily till you can test the ammonia levels.

What kind of filter do you have?

Don't put in any more fish till the tank is cycled. I would put the plants in now, though.