Contacts are part of leads, accounts, and Vendors. 

To add more contacts to one of the above elements, follow these steps:

1- Simply locate the lead, account or vendor.

2- In the details page, locate the sub tabs "Contacts"

3-Click "Contacts" to view all contacts related to this lead, account or vendor.

4- Click "Add Contact" to add a new contact.

5- You can create a new contact or search and link an existing contact.

6-  Click "Save"