How could I build a class system with abilities and skills like D&D?

D&D Classes/Skills system

thats a way to in depth topic to answer here. look into some tutorials on creating skill trees, progression systems, and character classes. if you have a more specific question then ask away but what youve asked thus far is too broad in scope.

alright, I need to figure out how to set up attributes like strength and dexterity and such in a way that progresses with a level system with a certain number of points allowed at specific levels to upgrade them

that shouldnt be too hard just have a variable called something like skillpoints and have a custom event called add points. then every time the player gains a level you call the add points function which adds a certain number to the skillpoints variable. if you wanted to have a different number of skill points added per level then you could use an array to keep track or you could use a data table to keep track of many attributes depending on the system.