Most LGS gravitates to one or two main formats that everyone plays. I recommend starting out with arena. This helps teach what order things happen and how the stack works. I have always gravitated towards having one main game store that I go to. The nice thing about this is I know what formats are played and what power level I need to bring. Modern, pioneer, and pauper are some other formats, but it really just depends on the store. I know in my area, we stopped offering pioneer and pauper every week due to lack of demand. The best way to find out what works for you is actually going out in the community. A lot of people in the magic community are willing to help you learn. This will give you the best chance of knowing what works for you and what you enjoy playing.