Nobody will laugh unless you try and push a point that's very obviously wrong. Welcome!
That depends on the system you use. The
FAQ has a bunch of different systems listed and is a great place to start.
There are balanced (number of positive cards equals number of negative cards) as well as unbalanced (number of positive cards is greater than the number of negative cards) counting systems, each with their own advantages and disadvantages. There are level 1 systems (+/- 1 only), level 2 systems (+/- 1, +/- 2) and level 3 systems. Level 1 systems are the easiest but level 3 systems are the most accurate.
I use Hi-Lo, which counts 2,3,4,5,6 as +1 and 10,A as -1. It is a level 1 balanced system.
You want to count every card you possibly can. This is harder for single-deck games where the player cards are dealt face down (and you might only catch a quick glimpse) and easier for shoe games where player cards are dealt face up.