Just decided to do it one day. Had done some utility sewing (bags, pillows, odds and ends) since I was little so knew how to at least thread a machine and straight stitch. As mentioned in a previous comment, shirts mostly have the same basic construction, so I just got a pattern, some fabric, and started trying.

Instructions on patterns are obtusely written, with a lot of extraneous steps about basting and other nonsense that can usually be skipped, but everyone here is an engineer of some sort and should be able to figure it out. You cut out shapes, pin them together so they don't slide around relative to each other, and then sew in a line a fixed distance from the edge (seam allowance, usually 5/8"). Most machines have guide lines that help you maintain that.

There are a few trickier bits, like sewing along curves where fabric is bending two different ways at once (like sleeve/body joints) and using the "burrito technique" to topologically invert the yoke of a shirt for easy sewing, but youtube has plenty of videos to help.