You've pretty much got it there
IF you're playing 200nl the big blind is 2 so that is the minimum each player has to pay to play his cards. You have to raise by at least the previous bet so if the blind is $2 your min raise will be raising by another $2 to $4 thats the lowest raise you can make and you can raise to anything above that you can raise to $4.03 or $5.62 or $137.66 whatever you want as long as its in your stack.
If the blind is 2 and you raise to 8 you raised by 6 so the next guy if he wants to raise has to raise by at least 6 again
Hope its clearer to you now