First, navigate to the Contacts page from the Toolbox menu:
To create a single contact, click Create and fill out the fields:
You will have options at the bottom of the contact record allowing you to keep the contact private to your user or available for anyone in the account to see, as well as being able to edit the contact:
Contacts can be uploaded in bulk via CSV file by clicking Import and following the instructions:
A search box is also provided to quickly search contacts: