First click:
Second click:
OK. I'm not sure to understand the problem you encounter.
The workflow... You are supposed to start to write your tag and to look at the list of tags that will autocomplete, caracter by caracter.
If you want you can choose directly an already existing tag.
If the tag doesn't exist, you can create it at the bottom of the list.
Don't forget "OK".
Anyway : you should look here:
And elsewhere using the search function:
