I won't go into super much detail, but think of generics as functions over types that generate new types based on type inputs (gross oversimplification). Comparable to functions that take value and return values, also it happens before your program runs (during compilation/build time).

A ring buffer is just a normal buffer, except that when it "runs out" of space instead of overflowing or returning an error, it "loops back" on itself, and starts writing from the start. You can still grow it, if needed.

The nice thing about generics here is that it allows you to have a RingBuffer[string], RingBuffer[int], and RingBuffer[MyType] without having to implement them separately. The compiler will even take care of memory sizing/layout, and all the other razzledazzle.

As for performance, it's not fully related to generics, but a sibling comment explained the implementation detail and how it affects performance.