By default, user-defined fields allow you to enter up to 100 characters of descriptive information. You may choose to require entries to be selected from a list. To do this, check the box for the user-defined field on the left of the UDF Choices tab, then proceed to enter your choices into the list on the right (Note that you can delete entries by selecting a row and clicking "delete" on your keyboard).
If you've already entered values into these descriptive fields on specific lease records and you now want to create a list, you can populate all current values for that specific UDF by holding "Shift" on your keyboard and checking the box to the left of the UDF.
You may also create lists for the asset class and financial group fields, which may store up to 50 characters each.