If you are in the US, don’t trust any dimensions for wood. Buy a cheap caliper and measure to confirm. Personally, I prefer to work in metric to resist the urge to round to a nice fraction. That being said, measurements are always relative and wood is very forgiving so keep a few offcuts labeled and stored away to use as a reference.

As far as tools go: a cheap pull saw, square, hammer, and a steel straight edge will get you started. Harbor freight has some cheap entry level tools worth buying once to learn on. A drill would be my first power tool purchase if you don’t have one.