Chainsets
Chainsets come in a myriad of combinations.
The most important option is crank length and a careful study or advise of an experienced rider or coach will ensure you use your leg muscles optimally.
The number of chainrings and size is also important. The PCD of the ring bolts limits the possible ring sizes.
Bottom bracket fitment is also a confusing factor these days. Ensure your frames bottom bracket shell can fit the required bottom bracket for the chainset you buy.