Assuming the Contractor is basically a Vendor who is invoicing you, You'd go to the Vendor tab and add new.
When they Invoice you, you'll go to +New and add a bill for that Vendor.
Customers are basically the same. Add them as needed and then when you Create an Invoice you'll do it for those Customers you've done work for.
Hi there, @nikki-premiercra.
Let me join in this conversation and help you set up your contractors in QuickBooks Online (QBO).
There are two ways to add your contractors into QuickBooks, you can either go to the Workers tab or Expenses menu.
From the Workers menu
From the Expenses menu
In case you need to edit their information or deactivate their accounts, this article would be a great reference for you: Add, edit and inactivate contractors in QBO.
I'm always here to help if you have any other concerns or questions. Just tag my name in the comment section and I'll get back to you as soon as I can. Have a great weekend.
Here's a quick video on adding Vendors, if the "Contractor" is truly a Vendor as I was thinking. This would be a Contractor that puts in a new sidewalk or something like that where they are going to Invoice you for their work on a individual projects.
If you are a Builder/Contractor and you're looking to add Sub-Contractors for a project, then use the instructions that @ReymondO gave you.