Creating a Custom tag is useful when you want to have a tag that doesn't appear in the core collection of ready-to-use tags provided in the app. A custom tag can be filtered on quickly using the app or dashboard. A custom tag will not however be included in charts created by the dashboard.
To create a custom tag, create a new board and tap 'Add Tags'. Swipe all the way to the left until the Custom Category is selected. Tap the Create Custom Tag button and follow the 3 steps below.