Manually enter data into a mapping table

I want to create a mapping table to map each distinct value of a column in a query with a more general category that I will specify manually. So I would get the list of distinct values with the DISTINCT function into a table, but then I'd like to add a column where I can specify the target value.

Now I can create an entire table by entering data, but I can't find how to manually add data in a new column of a table.

How should I proceed?