Watcdy -  Delta is a measure of how much the option price will move in relation to a move in the underlying. It's complicated but imagine that you are short a 16 delta call in SPY. In order to neutralize the trade (sort of), you would simply buy 16 shares of SPY against 1 short call...but then you would have to adjust as conditions change.

I definitely wouldn't recommend jumping into SPX credit spreads (short puts and calls) until you get some options trading under your belt with smaller instruments. Try "TastyTrade.com" for education. It's a great site and community - almost but not quite as good as this one ;)  Including a screenshot of a short SPX trade I would put on today, if I wanted to add more shorts. Note the trade characteristics in the left hand column. You can get your a!@ handed to you pretty quickly, if you aren't careful. The short call in this example is currently about 16 delta.