how do i choose the right keywords for your website properly?

Map them to pages rather than collecting a big list. For each page on the site, one main keyword plus the close variations, and the main ones shouldn't overlap or two pages end up competing. Where to find them: Search Console if the site's been live a while (you'll see what you already get impressions for), Google autocomplete and People Also Ask, and a keyword tool for volumes. Newer site? Lean towards longer, more specific phrases, they're far easier to rank for and usually convert better anyway.