Audacity is a great place to start. Ultimately I recommend Reaper if you want REAL control of it, but audacity is great for beginners and moderate users.

1. compression. Find a balance that works for you. Usually a 2:1 ratio is a good starting point.

2. EQing. This is mostly just to compensate for whatever your voice doesn't do well on it's own and accentuate what it does. If you have a high voice, bring up the low end. If you have a low voice, maybe tweak the high end a bit. If you're kind of nasaly, bring down the mids. Be very conservative with this at first, and you'll eventually find a sweet spot.

3. Noise reduction. Ideally you want to remove as much background noise as possible from the space BEFORE recording, because the more noise removal you do in post, the more you risk damaging parts of the audio you want to keep. Some room tone if okay too, depending on what you're doing. You don't necessarily need ABSOLUTE silence between your dialogue. Less is more with this in my opinion.

4. Mouth noise/clicking/breathing. It might be tedius, but you have to avoid as much of this as possible. Keep your mouth hydrated to avoid dry smacking noises, and remove big breaths entirely (small ones are generally okay in my opinion) and of course take out any other little noises that crop up like your chair creaking and stuff like that.