a 'tech', when not talking of advanced techniques, is when you press the shield button right before you hit the ground, a wall, or any other solid obstacle after being hit. If you are still in knockback and don't tech, you'll either land on your face(if you hit the ground) or bounce off(if you hit something OTHER than the ground)
Pressing the shield button alone results in a standing tech - your character simply hits the ground and pops up into a neutral stance, or hits a wall/ceiling and cancels all momentum, returning to a neutral(aerial) stance.
When you tech from the ground, if your press right or left at the same time you hit shield, your character will instantly roll to that side before standing up. On a wall, you can press jump at the same time as shield to do a wall jump, even if your character can't do a wall jump.
Tech chasing is predicting the tech, and moving to that location and attacking the instant the other person become vulnerable. Game&Watch can down throw, then run left/right, charge an upsmash, and release as you end your tech-roll, IF they predicted the right direction. Or then can down smash if you tech in place.
If you miss a tech(or are in a situation where you fall on your face without a chance to tech, like ganondorf's side B) you have similar options - roll left or right, get up in place, or get up in place while attacking. A good ganondorf might predict your response, and use Side B again in the direction you roll, or step away from your get up attack and use it again. This is also called a tech chase, even though there is no real teching.
knowing how to tech consistently is just that - having the timing down for teching.
edit: that was rather long for 3 questions
