These are called stringers. One way to do them is to buy them pre-made at a home improvement center. If you want to make your own here is a site with a calculator to figure your measurements: https://www.mycarpentry.com/stair-calculator.html. If you cut your own be sure to follow building codes because they are very precise. Perhaps the best way is to hire somebody to cut them for you. The cost probably wouldn’t be too high for this.