To quickly block an email address as a spam sender, swipe the email and choose the 'Spam' action. This will move the email to the spam folder and also block the sender's email address.
The spam popup screen that then appears has a button for more options for blocking similar emails.
When a spam sender address is blocked, all future emails from that sender address or domain will be sent to the spam folder automatically.

Make sure the 'Simple Spam Block List' rule is turned on to move new blocked emails to the spam folder. Details

You can also manually block an email sender address or domain. Tap on the 'From' address in an email to open the sender detail screen.
In the bottom of that screen you can tap on the 'Block for Spam' button to block an address. You can block the email address domain too. You can unblock an address or domain that is listed as blocked by tapping on the 'Add to Spam Safe List'.

Tap to open the 'Spam Check' section. Then in the spam screen you can tap on the 'Block for Spam' button to block an address.
Open the Spam Analysis section of the details screen to see more options. You can block the email address domain too. You can unblock an address or domain that is listed as blocked by tapping on the 'Add to Spam Safe List'.

You can manually edit the Spam Block List in the app settings screen. View. Then open the Spam section. Then you can tap on Spam Block List or Spam Safe List. You can add or remove email addresses or domains in each list.

When you send an email, the recipient address is added to the 'Known Senders' list which is also checked as part of the spam rule checking. Open the app settings (View) - Spam - Known Senders.