To use the LINEST or LOGEST function in Excel, follow these steps:

1. Open the Excel application.
2. Open the spreadsheet containing the data you want to analyze.
3. Highlight the desired range of cells for analysis.
4. In the Formulas tab, click the drop-down menu under More Functions.
5. Select the Statistical function from the drop-down menu.
6. Choose either LINEST or LOGEST from the Statistical menu.
7. Fill in the necessary data fields.
8. Click OK to finish.