It's a fonetical rule:
- Palabras agudas (last sylabe sound more strong): they are acented in the vowel if they finish in s, n or vowel
- Palabras llanas (penultimate sylabe sound more strong): they are acented on the vowel when they don't finish in n, s or vowel.
- Palabras esdrújulas (antepenultimate sylabe sound more strong): they are acented in the vowel always.
Sorry if I use an English not too much good, but I have forgotten it too much.
And welcome to the forum!!!
'Prever' is a verb easy to conjugate, though many people make mistakes when they confuse it with the ver 'proveer'.
Pre+ver = ver con anticipación.
It is conjugated exactly the same as 'ver', but with the prefix. The accent, the strong syllabe is always the one that would be strong in 'ver'.
'Ve' doesn't have a written accent because it is a monosyllabe.
'Pre-vé' has a written accent, it follows the general rules.