You have two ways to add your vendor details in QuickBooks Online, @UniIlo. 

You can either add them manually by entering all the vendor details in the required fields, or import them to enter their complete details in bulk automatically. 

Here's how:

1. Go to the Expenses menu, then select Vendors.
2. Click the drop-down menu in the New Vendor tab on the upper right. 
3. Select Import Vendors.

From there, choose either you want to upload a .CSV file or from Google Sheet. See sample screenshot below:

For further insights, you can visit this article to learn more about managing your vendors in QuickBooks.

Feel free to ask more questions if you have any. I'll be there to answer them.