Maybe get started by researching online how to build an endless loop string and the jig required for it. The jig can be purchased through suppliers like 3Rivers and others or can easily be built if you are handy and have access to some basic woodworking tools.
The B50 Dacron has been an industry standard for many years and is perfectly fine, and you can move up to thinner (faster) materials with less stretch like FastFlite, AstroFlight, Rampage, etc., as you become proficient. The serving material is also sold by all the suppliers, and again is available in many different materials. Basic nylon is acceptable and the cheapest way to get started, in many colours. And you’ll need a serving tool. Good luck and have fun, they really are quite easy!