Hello, @jodage.

You can use a Job Name or Job Number to denote the specific job you're currently working on. Let me guide you how to track jobs in QuickBooks Desktop.

1. Go to the Customer menu.
2. Choose the Customer Center.
3. Select the New Customer & Job drop-down.
4. Pick Add Job.
5. Enter Job details.
6. Click Ok.

On the other hand, a billable expense is a specific expense and/or time entries you incur on your customer's behalf especially when you perform a job for them. Here's how:

1. Go to the Vendors menu,
2. Pick Enter Bills.
3. Type in the Bill details.
4. Make sure to put a checkmark on the Billable column.
5. Assign it to a specific Customer or Job.
6. Click Save and Close.

Once you create an invoice for the job, you'd be prompted by QuickBooks there's an outstanding billable cost assigned to it. 

However, if you're using QuickBooks Online UK, the billable expense feature is only available in QuickBooks Online Plus only. You'd want to turn on this feature in your account settings. Here's how: 

1. Click the Gear icon.
2. Select Account and Settings.
3. Go to the Expenses tab.
4. Click the Pencil icon in the Bills and expenses section.
5. Check the Make expenses and items billable box.
6. Select on how you track the billable expenses and items as income.
7. Click Save, then Done.

You can read through this article for more detailed steps: Enter billable expenses.

Let me know if you have other questions about using QuickBooks in managing your job expense transactions. I'm always here to help.