Web/Desktop/Browser extension:

• Right-click on an item and select "Manage tags"
• Enter the name of your tag and hit the "Enter" key
• Apply your changes

Android:

• Open the more options menu for an item
• Tap "Manage tags" and then "Create tag"
• Enter the name of the tag and confirm
• Save your changes

iOS:

• Open an item and tap "Edit"
• Find the Tags section and select "Add tags"
• Enter the name of the tag and confirm
• Save your changes

If you want to add a tag to multiple items, select these items and open the "Manage tags" (iOS "Tags") menu.

You can create only 1 tag at a time. However, you can select as many existing tags as you like.