The two words mean the same thing, the alphabet is known in Spanish as: el alfabeto or el abecedario. The Spanish language is written using this alphabet.
One of the most important things in Spanish when speaking is the correct pronunciation and separating the sounds of letters and vowels very well, since almost all sounds are independent.
In Spanish we had 29 letters until 2010, including: Ch (ché), Ñ(eñe) y Ll (doble l), however, the Royal Academy of the Spanish Language (Real Academia Española RAE) considered that (Ch and Ll) were not letters per se, but a composition of two letters. Now we have 27 letters: A, B, C, D, E, F, G, H, I, J, K, L, M, N, Ñ, O, P, Q, R, S, T, U, V, W, X, Y, Z.
We have 5 vowels and 22 consonants :)