In HealthFrame v2, the simplest way is to go to Reports > Expenses > Expense Register, and click the "Add New" button.
Then you can create a bunch of expenses and see them summarized in Reports > Expenses > Transaction Report.
Plus, most other objects you track (e.g. medications) have 'shortcuts' to add related expenses.
Also - you may want to load the 'Susan Taylor' sample PHR that comes with HealthFrame. It has some sample expenses you you can see the expense report without entering any data.
Hope that's enough to get you started!