If you wish to create a custom tag for your Campaigns, it is possible with Edit Tags button.
Simply choose a Campaign you wish to create a tag for and click Edit tags. A new field will open where you can enter your custom tags. Do not forget to separate tags by commas. Click Save when you're done editing.
After that, you will be able to filter Campaigns by their tags:
Should you have any further questions, please contact firstname.lastname@example.org and our team will be happy to assist you. Happy tracking!