To add a new Vendor you just select 'Companies' within the CRM tab in the left navigation bar.
Next you'll want to select the green '+ Company' button in the upper right corner. Then you'll be able to add all the Vendor information. Make sure to set the 'Company Type' to vendor as displayed in the following image.
Once you've finished adding all the required information save the Vendor and now you'll have that Vendor as an option within your TRACK system.