We're going to talk about what CC doesn't cover!

Probe (HELP PROBE) is your friend.

TN “TARGET NUMBER”

A target number (Commonly referred to as a TN) is the number you are rolling your dice against in a specific test. Shadowrun is a D6 system so numbers are generally in single digits. A standard TN for a 
test is 4. If any dice are rolled equal to or higher than the TN it is classed as a success, though any roll of 1 is counted as an automatic failure, no matter what the TN is.
 
For TNs higher than 6 you must first roll a 6, then another number that when added to 6 would be greater than the TN to score a success.

So why is this relevant?

Because penalties.

There are a number of mechanical aspects in the game that will either improve your TN (by lowering it and making your life easier) or raising it (and making your life harder). We'll be covering the more common ones. The other important thing to keep in mind is all these and more affect both mobs and players! It's not one-sided. Use it against the mobs.

1. Vision: Is it too dark (HELP SURVEY and HELP TIME)? Is there mist? Is there smoke? How far away is your opponent? Are they invisible? Having the correct vision for the job is super important, with the 'stronger' vision types having higher penalties and their own requirements, but allowing you to see in worse environments. Thermographic vision's penalty is greater than astral vision's, but the penalty for thermo only applies to attacks - the penalty for perceiving astrally affects everything.
2. PAIN: How injured are you? Each level of damage has a different size of TN penalty, getting worse as your injuries build up. This is what makes pain editor so useful, since it allows you to ignore this entirely.
3. Cover: How much cover is there? Your character will automatically use room cover (SURVEY) to duck behind and avoid ranged attacks.
4. Prone: Going prone improves your ability to shoot things (and not get hit) at range. Be careful, because that effect reverses if they're in the same room as you.
5. Background Count: This is more for against mages and to use against them, but killing a lot of mobs/casting a lot of spells/standing in an astrally active room has a higher background count, which makes casting spells tougher.

Natural or Magical version > equipment or cyberware version. Natural thermographic vision is better than thermographic from an item.

This directly affects your TNs for taking damage. Body is how many dice you have to roll to reduce damage.

That about does it. Now go out and kill some people.