Go to Google Contacts at contacts.google.com
Sign in with your Gmail account
Select the contact you want to delete
Click the More actions menu
Choose Delete
Confirm the deletion
To delete multiple contacts, select several contacts first
Click the More actions menu
Choose Delete
Confirm the deletion
To delete all contacts, select all contacts in the list
Click the More actions menu
Choose Delete
Confirm the deletion
To remove contacts from a label, open the label
Select the contacts
Click the More actions menu
Choose Remove from label
To restore deleted contacts, open Google Contacts
Click Trash
Select the contacts
Click Recover