In some movesets for Pokemons I saw words like priority and Stab and stuff but I don't know what priority means
All moves have a level of priority.
Most moves like Thunderbolt are what we call Stage 0. This means that it has 0 priority.
Moves like quick attack have +1 priority. Moves like Roar have -6 priority meaning unless another Pokemon is using a -6 priority move it will move last.
Likewise a Pokemon using Quick attack no matter the level will move before a Pokemon using Thunderbolt.
This link has everything you need to know.