If you don't need or want all of the default columns, you can either rename them or hide them out of view.
Do NOT delete Columns.
- This will ensure you don't accidentally remove formulas used to calculate your hours. Always "hide" columns and never delete them.
To hide unwanted columns you don't use, right click on the Letter at the top of the column (e.g. "AA") and select "Hide".
You can unhide the hidden columns by highlighting the Letters at the top of the column either side of the hidden one (e.g. in this example, highlight "Z" and "AB"), right click and select "Unhide". Column "AA" will now reappear.