One way to block a sender is open the menu at the top of the inbox by clicking the 3 dots,
Select Filter Messages
Make sure the From is correct and click on create filter at the bottom
Select the box "Delete it"
You may also select the box at the bottom to apply to additional conversations if you already have more than one
if you are getting spam emails from multiple people at the same domain(the part after the @), such as notifications@facebook.com, alerts@facebook.com, etc., you can put and asterisk (*) before the @, like *@facebook.com. This is called a wildcard and will deal with any sender address from @facebook.com
Click create filter at the bottom
Senders meeting the rule will automatically be deleted and you will not see them in your inbox.