You may be looking to give your spreadsheet users a quick drop down from which they select a value. You can create this feature in a few, simple steps.
You start out by going to the Data menu and then selecting Data validation. Note that you have to be on the desktop version of Sheets to create this drop down. There is no Data validation option in mobile Sheets.
Once you have selected Data validation, select the List of items option.
Type the different values for your drop down.
You're done! This drop down will always be in this cell with exactly the values that you entered. If you want to change the values, you will can go back into the Data validation options and change them from there.