A base is a rule for writing numbers. Once you understand what each position means, you can read any base.
In base N, each position represents a power of N: from the right, N⁰, N¹, N² and so on.
For example, decimal 255 is 2×10² + 5×10¹ + 5×10⁰.
Computers use binary (just 0 and 1), people use decimal, and programmers use hex as a compact form of binary.
Base N uses digits from 0 to N-1, extending beyond 9 with the letters A (10) to Z (35).