You can add tags to files either individually or in bulk in Speak:

Visit your file and select "More" in the top right.

Then, select "Edit" and a pop-up will appear.

You can create new tags or select from a list of tags in the account.

If you write the tag, hit "Enter" on your keyboard after to finalize it.

Once done adding tags, you can hit "Update" and the tag will be saved!

You can then see the Tag below your file name.

You can follow the same process but instead of viewing an individual media file visit your folder and select "More" and "Edit" for the same pop-up and function.

When you hit "Update", that will be saved across all files.