Hi, welcome to iPF!
You can't block email addresses on your iPad using the Mail app. What you can do there is move the emails to Junk/Spam, but you'll still receive them.
You'll need to check if your email provider allows to block emails. If you can access your account using a computer, do it there. On your iPad, it's possible to view the desktop version of Gmail, Yahoo, Outlook, ... using Safari. Note: Gmail doesn't allow blocking email addresses currently. What you can do is keep them out of your Inbox.
Some emails give the option to unsubscribe to a newsletter,... at the bottom of the email. If you find this, use the link provided there.