If you are an Administrator or Manager (or Contributor with the right permission) you can upload new Vendor Companies and Contacts. You can also add either manually if you just have a few.
For manual add, look for the orange New Contact button in the Contacts page. You'll need to add the Company first, if it doesn't already exist.
To add Contacts, go to the Contacts page in the same Vendors Module area.
You can add Contacts individually using the orange New Contact button, or you can upload Contacts in bulk. For bulk uploads, click on the Upload Contacts link.
Here's an example with some fake names and email addresses. You'll also need Vendor names in there, so the system will know what Vendor (organization) the contact belongs to.