I actually have a 30 year old bike that I've already done some stuff to, but I had to adjust the front and rear derailleurs when I put this bike together - it took me around an hour or so, but the rear cassette shifts now as opposed to getting stuck between two gears. I also adjusted my breaks (the pads would rub on the disks at a stop, but I managed to fix that)
I desperately wanted a car to work on and fix up, but I guess a bike will work too! ๐
I'm also struggling to understand ๐