New to Mastodon, these guides can help.
https://dev.to/zkat/kat-s-mastodon-quickstart-for-twitter-users-39db
https://2ality.com/2022/10/mastodon-getting-started.html
https://www.youtube.com/watch?v=mrsiej2dpBY
You can skip the signup process or register here, it will be the same.