You don't include a screenshot so just guessing but it seems like you have defined columns A, B, and C as Header Columns.
You can insert three non-header columns, copy the data over from the Header Columns and then delete the Header Columns. Then when you scroll to the right those columns won't stay in view.
Question: Header Columns are very handy, so often one wants them to stay in view. Why would you want them to disappear from view off to the left?
If you're just starting out with Numbers, or even if you are experienced, you will find lots of good explanations and Help > Numbers Help in your menu. Highly recommend spending some time there.
SG