Ive got a couple of questions
firstly…
how often should u change your strings? Ive been changing mine after about 10hrs of play. and secondly…
The differences between strings? I s there strings specifically designed for types of tricks, ie looping and string
Change the strings whenever you want to. Whether it be from fraying, breakage, whatever.
cotton is best for looping
i change mine every 20 min or so
Change it when you feel like it. I go several weeks at a time with one or two.
Opinion.
I change mine every few days. The different types, thickness, twisting, material, and everthing else effect the string. Cotton only lasts me about 30 minutes while some Nylon lasts me a few days. It is really all preference, and the string you use depends on what kind it is and how often you yoyo.
I use Perfect Fit and change it once a week or so… as it get old with alot of use it develops bad tension very fast as compared to when it was new so then I use the old string for 5A because I dont do alot of 5A slack…
I broke a cotton in 30 minutes… I was bummed… Burned through a whole 5 pack in a day
For 1A, I’m using 100% polyester right now and it lasts me about 15 hrs of total play. Some other stuff from G-string has lasted me up to a few days (ie. SSE, TH, and INT formats).
For what types of strings are better for different types of tricks/ different styles of play, it comes down to testing them out for yourself and deciding based on what you find. For me, almost everything is fine for string tricks (excluding slacks, suicides, whips), but I find 100% polyester performs slacks, suicides, and whips really well, and after that I would go with 50/50.
Haven’t tried the polyester nylon mix yet though so I dont know how those play. Again, buy some for yourself, and test 'em all out.
Hope that helps! 
I’ll put in my two cents. but its all really about how you feel about the string. If its getting dirty then change it. Really if its affecting your play change the string. The differences between cotton, poly, and nylon are preferences. Most people like slick string for string tricks while having something with more of a feel (cotton) for loopers. There’s no real rules on when to change them. Change them when you want to.
Cotton does break which is why people usually stray from using it. So sometimes people get poly/cotton mixes. Look around see if you find something you like, most string is cheap so get a 5-6 pack and use them. if you don’t like it don’t use it. Hopefully this helps you out.
String is changed by your opinion. Though it’s recommended to change the string often. I don’t change my 100% poly string often cuz all 100 of them have to last me a year(my stepdad buy’s me them every 1st of december)
different types of string of course are meant to perform different tricks. many advanced players prefer 100% poly or a poly/nylon mix for 1A. Cotton isn’t prefered by many because it isn’t very durable and many say it plays “cheap”. Yoyoexpert.com recomends Slick6(cotton/poly mix) for beginner players, intermediate tricks, and looping or 2A. but just because of a few recomendations doesn’t mean you HAVE to use it for this and that. It’s all about preference.