Actions blocks are tasks that you want to fire from your side for the target contacts within a funnel. Email Marketing has several action blocks:

Wait X Days/Hours
Wait defined timespan before executing the next action.

Apply List
Add this contact to the selected lists.

Apply Tag
Add this contact to the selected Tags.

Remove From List
Remove this contact from the selected lists.

Remove From Tag
Remove this contact from the selected Tags.

Update Contact Property
This action lets you update custom contact properties for the contacts within the automation.In order to update a custom field, simply Select a Contact Property from the dropdown and add the value you want to update.

Add Notes and Activity
This action lets you add custom notes and activities for the contacts within automation.
To add notes and activities to the contacts in your automation automatically, select this block. In the pop-up window, select your contacts Activity Type, give a Title and write your description.

End This Funnel Here
If you apply this action then no further action will run once a contact hits this point. This automation will be marked as completed in this point for a contact.

Send Custom Email
Send a custom Email to your subscriber or custom email address.

Set Sequence Emails
Send Automated Emails based on your Sequence settings.

Cancel Sequence Emails
Cancel Sequence Emails for the contact.

Send Campaign Email
Send an Email from your existing campaign.

Cancel Automation
This lets you cancel automation for the contacts within your automation