On your Home or Workspace page on the app tap on the ➕ on the bottom.
You can also add an expense from the expenses page.
Tap New expense.
Enter in the relevant information for the expense.
If you have a photo of your receipt, you can add an attachment from your camera roll. Tap Upload attachment and then either take a photo or browse your photos or documents.
You are shown a summary of your expense request. You can add another or tap Close.
Once you're done, whenever you browse to expenses, your expense is listed as waiting for approval. Once approved or declined, the status will change.