It depends on what level you're starting from. During non-COVID times, a reasonable path was to buy a sewing machine from a local shop and part of that transaction would be a short class to help you understand and use your machine. Nowadays, that may be difficult, but depending on your timeline that may be an option in the future. On a similar lines, a good fraction sewing machine shops and fabric stores offer classes, which can also be incredibly helpful. Generally, the progression is something like intro to sewing and then intro to garment sewing.
If you've never done garment sewing before, an apron is a good first project. It'll get you used to your machine and how to sew some simple hems and run a draw string. It's also something that's usable, which is nice. After that, pajama pants are a reasonable starting point to the world of pants. Really, any simple pattern should be fine, so something similar to this:
https://www.simplicity.com/simplicity-storefront-catalog/pat...
The key point on pajama or lounge pants is that they don't contain pockets or a fly. However, they do give practice on how to sew all of the fabric together on the crotch, which can be tricky to start. To add a fly, you'll have to learn how to sew a placket as well as how to either sew buttons and button holes or a zipper. Again, neither is particularly difficult, but they do require practice and there a lot of tricks to make it easier, which is partly why a beginning sewing class is nice. To add pockets, it depends on how nice you'd like it to look. Patch pockets have their own set of technique and how to interface, but are the mostly straight forward. You can substitute rear patch pockets with welted pockets and there are good online tutorials for those. As far as the front, I'll contend that slash pockets are easier than a j-style pocket that jeans typically have. Basically, the more complicated the pocket, they more pieces and interfacing that's required and it can be a pain.
If you really want to go the online route, Thread Theory has reasonable patterns that can be downloaded:
https://threadtheory.ca/collections/sewing-patterns
As far as traditional pattern makers, stuff from Simplicity is pretty simple, but stuff from places like Vogue is a pain.
Ok. That was an overload. Bottom line: (1) Get a machine (2) make an apron (3) get a pattern for pajama pants (4) slowly add features to your pajama pants until you want to make nice pants (5) get a pattern for nice pants (6) classes help a lot. Iterate on that as long as you're having fun.