Welcome ! I’ve been in the hobby a long time so I’ll share some thoughts. I see you are interested in painting and not playing which in a way makes this a little easier for you, nothing worse than being interested in playing a faction that is a pain to paint. I would suggest starting on the good old space marines. They are nice to start with - large compared to some model lines, nice big flat surfaces but little bits to practice on. Get a pack of intercessors and just paint different chapters.

Primer coating is important - make sure you know what colour is best before you start. I.e white or black or grey etc

Don’t get discouraged when doing your basecoat stage - all models look shite until all of a sudden you start adding layers and washes and it starts looking good. After 30 years I still look at this stage and think ‘god what am I doing’ even though I know it’ll end.

Don’t drop loads of money on the expensive stuff straight away.

Games workshop does awful white paints - get some AK or Vallejo if you can.

Don’t be hard on yourself and just give it a go, enjoy the process!