The Bulk Actions option makes it easier to select and perform an action on a group of records in bulk. 

i. On any view of contacts or companies, select the checkbox right before Basic Info
ii. A banner above will ask if you want to Select All Contacts. Click on the link to select all contacts. 
iii. Once selected, go to Bulk Actions on the right side of the screen. From the drop-down menu, you can select the action you want to perform in one shot. 

The types of actions that you can perform on a large number of selected contacts:

Add Tag
Delete Tag
Add to Sequence
Add to Broadcast
Send Email
Send SMS
Add to Static List
Send Double Opt-in
Marked as Confirmed
Validate Emails
Export as CSV
Change Owner
Execute Workflow
Call Broadcast
Remove from Sequence
Remove from Workflow
Send Push Notification
Update Fields