The single select field is perfect for when you want to select a single option from a preset list. For example, you might want to input a preset list of departments in an organization or status for a case management backend.
To create a new list of Single line items, you can click to add a new field type, add a name to the field and scroll to the Single line field type. From here, you're able to click on the "+Add an option" button and type in free text into the new option and set a color for the option by using the dropdown arrow to the left of the option.
You can edit your options once the field has been added by clicking on the customize field type option.
Once you've created your field, you can choose which record gets what value by clicking on the cell in the corresponding record and clicking the downward facing caret. This will allow you to choose from one of your options.
You can also edit the cell contents for a record by using the expanded view.