When you enter keywords on GN4 forms, GN4 assists you by displaying, for any letter you type in the field (1), the list of approved keywords (2) that start with what you typed so far. So on the following screenshot, you see the list of all keywords that start with "wild".

Note: if the list is empty, it means there's no such approved keyword, and then you can decide what to do.

When you identified the keyword in the list, you click it (3), and then click the + button (4) to accept it. It appears in the field (5).

You can proceed to add other keywords, it you want to. At any time, you can click in a keyword you don't want anymore (5), and then click the - button, that will remove it from the field.