Assembly isn’t the only language that can be used to program a 6502 based computer! Another language that can be used is C. One of the main advantages of using assembly is that it is the fastest language (unless you write in machine code!). However, C is worth using and there are lots of optimisations that can be made to speed C code up. If you want to learn C, then I have a course on C: C.
C is a compiled language and therefore we need to use a compiler. When the program is run through the compiler it is first turned into assembly language and then into machine code.
There are a number of suitable compilers available, the one that I use is cc65.