I can’t decide what kind of string to buy 
Keep it simple when starting. Most people use 100% poly for string tricks or 50/50 cotton/Polyester. Cotton string if you are looping with fixed axles, polyester will melt.
Premium strings play a bit differently but are more expensive and until you have played for a while you probably wouldn’t notice any difference other than the price. Some people never use premium strings and others swear they are the best. It’s really about preference.
Conclusion: Probably 100% poly or 50/50 cotton/poly for the time being, and check out different types as you go.
Good luck!
not cotton prolly what ^ said
Yup. Keep it simple to start. I’ve got like 400+ extra strings of YYE 100% poly and it’s good enough for me for now. No complaints and no issues. I also have a 100-count of 100% cotton and 50/50 so I’m good for almost anything that comes at me.
Once you’re thinking of changing strings, buy a bunch of small packs of a bunch of different stuff, at least 5 counts, 10 is better. Then, see what you do or don’t like from that. Just keep track of what you’re playing and what you do and don’t like about it. Once you narrow it down, chances are you can pick a stand-out string and bulk up on that.