When I first started using jigs it was over whelming as well. They can be used almost any conditions. When fish are active use a swim jig or fish a football jig fast " hop" it. When the fish are not active use a slower technique/retrieve in this case.
As far as trailers go, I always use them, they add more bulk to the jig and make it appear more life like. They also add action to the jig. However in a case like a slow day or the fish are not liking a trailer I will take it off..... Let the fish tell you what they want.
This is jigs in a quick sum, this is a big topic..... My best advice would be to take each jig and spend a week with it and just dig that , learn each and how it handles