I have added a new expence , but I dont know how to make a new income category for it?

It's nice to see you in the Community, @willoglenwaterco.

There are three ways to set up a new income category. From the transaction's screen, Income Account drop-down of your product and services, or in the Chart of Accounts window. Let me walk you through the steps for every option.

First off, you can create a check. Here's how:

1. From the Plus icon or +New button, pick Check.
2. Fill out all the necessary information for this entry. 
3. In the Category column of the Category details section, click the drop-down arrow and choose +Add new.
4. Select Income as the Account Type.
5. Choose a Detail Type from the drop-down. 
6. Name the account.
7. Hit Save and close.

The second method is by adding an item. Follow these steps:

1. From the Gear icon, select Products and Services.
2. Click the green New button.
3. Select your item type.
4. Fill out the rest of the item details.
5. In the Income Account drop-down, pick +Add new.
6. Then, follow the steps above from 4-7 to complete the process.

The third option, which is the easiest one, is by going to the Accounting menu. 

1. Pick Accounting from the left navigation, then select Chart of Accounts.
2. Click the green New button.
3. Perform the same steps above from 4-7 to set up the account.

I'm adding these articles for your reference: 

• How to write checks.
• How to set up products & services: Non-inventory, Service Items, & More.
• Create a new account in your chart of accounts in QuickBooks Online. 

Post again in the Community if there's anything else you need. I'm here keep helping. Have a great day!