Starting a Mastodon instance
Choose a plan from the pricing page.
Fill out the form with the domain/subdomain you want to use and your email address.
Follow the link to make the payment via PayPal.
After the payment is received
If you chose to use your own domain/subdomain you will get an email with the DNS configuration instructions. If not, you will only get the second email.
You will get an email informing you that your instance is ready and asking you to create an account and indicate the username to make admin.
Notice: during the night in Western European Time (WET) the install will only start the next morning.