Just start. Most shirt construction is based on a two-piece collar, a yoke, and button front. I started with a cheap pattern (McCalls 2447) that covered those aspects, and started modifying from there, but any dress or sport shirt pattern will give you the same basic construction.

Any machine will do. I had borrowed a cheapo Singer Simple machine from my father in law to make some pillows. Reverse lever broke on my second shirt, made a new one with some D-shaft and coupler from Mcmaster-Carr and still using it.

First shirt was recognizable as a shirt and sort of fit, second shirt was better, and by the third I had mostly dialed things in. Like any skill, practice makes perfect. Mostly sewn woven fabric, except for some TOS tunics with the velour knits. Made a pair of pants that I wasn't happy with and intend to loop back to that one of these days. Thing is, wild fabric is more appropriate for shirts than pants, so that is where I have focused.

My various works https://dave.org/sewing/

Not the commenter you asked but I inherited my mother's sewing machine and decided to make a ball cap by seam ripping apart one that was wearing out but fit really well.

I traced the pieces onto new fabric (waxed cotton) and reused the existing plastic brim insert. It's still in use and I enjoy telling people I made it although there a few things I'd do differently. I watched a few yt videos on constructing a cap for tips on things like machine settings, top stitching, fastenings etc then just winged it after I felt like my theoretical knowledge had plateaued.

It would undoubtedly have been cheaper to buy a new cap, but since I'm unemployed, long term burned out and also newly-diagnosed with ADHD, some things are just gut feeling without making a great deal of sense these days.

Now as things wear out I'm cutting them apart to study the pieces and make new versions. It's surprising what you can make. I just made some quilted slippers for my kid by tracing around his feet and using scrap leather I had lying around. My next project is a pair of trousers. Weirdly, as a recovering perfectionist, I find myself a lot more open to making prototypes and learning from mistakes than I ever was in my career.