1. Make sure your map is at least decent by modern standards. You seem to be a new mapper, so this is probably where you'll get stuck for a while. Nevertheless, I think it's good to know how the process works.
2. Make sure your map follows the
Ranking Criteria.
3. Get two
Beatmap Nominators to
nominate your map.
During the process, you'll likely get other people to
mod your map in order to increase its quality. I didn't give modding a step of its own since it's a part of each of the steps I mentioned.
e: oh god I didn't realise the wiki page for modding was that outdated