Where do I find the class and categories in QB online?

They are turned on in company settings = advanced, if you have the plus version

The tracking categories (classes and locations) options are only available in QuickBooks Online Plus, kamini. 

You might want to upgrade your subscription if you're using QuickBooks Online Simple Start or Essentials.

Here's how we can turn on the class function:

1. Click the Gear icon in the upper-right corner and select Account and Settings.
2. Select Advanced tab and go to the Categories section.
3. Mark the Track classes box.
4. Then, choose how you want to assign the classes.
5. Click Save and Done.

Now, here's how you can create a class:

1. Click the Gear icon in the upper-right corner and select All Lists.
2. Choose Classes and click the New button.
3. Set up the class and click Save.

You can use this article for reference, too: How to Set Up and Use Class and Location Tracking.

Let us know if you have another concerns.