General navigation around a spreadsheet
To navigate across the different spreadsheets you can use the left and right arrow is at the bottom left hand corner of excel.
The monthly spreadsheets are large and to help navigate, the page is split into two. This is indicated by a grey bar across the middle of the screen. This can be selected with your mouse cursor and dragged and down to show more or less of a particular part of the spreadsheet. The sales are recorded in the top half, purchases in the lower half. Mileage is calculated to the right of the sales columns.
In general you can only alter items in red.