Hi there! I can definitely help you with that. It sounds like you have accidentally turned on the "Extend Selection" feature in Excel. This feature allows you to select a range of cells by clicking and dragging your mouse, but it can be frustrating if you don't want to select multiple cells at once.

Here's how to turn off the "Extend Selection" featu

1. Open Excel and click on the "File" tab in the top left corner.
2. Click on "Options" at the bottom of the left-hand menu.
3. In the Excel Options window, click on "Advanced" in the left-hand menu.
4. Scroll down to the "Editing options" section and uncheck the box next to "Extend data range formats and formulas."
5. Click "OK" to save your changes.

That's it! Now when you click on a cell, it should only select that one cell instead of a range of cells. If you ever want to turn the "Extend Selection" feature back on, just follow the same steps and check the box next to "Extend data range formats and formulas."