Excel's AutoFit feature is available in the Home tab, and you can apply it to change the column width based on a single cell or on an entire column of cells. When you use AutoFit on a single cell, the entire column width adjusts to that cell specifically, so the content of cells above or below it may still not fit properly. If you apply the feature to an entire column, the width fits the widest cell in it, so the content of every cell is visible.
Select the cell or cells you want to AutoFit or click on a column heading to select all the cells in that column. Click on the "Home" tab and then click the "Format" button in the Cells section. A drop-down list appears, where you can click "AutoFit Column Width."
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Rather than use AutoFit, you could instead use the Wrap Text option, which breaks a cell's text to continue onto additional lines within that same cell. This is available by clicking "Wrap Text" in the Alignment section of the Home tab. You may need to adjust the height of the cell afterward to display all of its content. Another possible solution is to merge adjacent cells so they appear as a single cell. After selecting one or more adjacent cells, click "Merge & Center" in the Alignment section of the Home tab.