There are two ways you can upload and attached receipt files/images to your Expenses in the Expense Tracker:
The first option to upload a Receipt is directly in the Add Expense modal window when you are intially adding the Expense.
The second option is to upload the Receipt directly to the Expense Tracker table after you have already added the Expense. On the far right side of the Expense Table there is an "Upload" button which you can click to upload a receipt to an existing Expense.