Using labels is one of the best ways to manage your emails. Add multiple labels to an email to track it easier. To add or remove label in Gmail for Android do as follows:
1. Open "Gmail" Apps (it is recommended to update Gmail to the latest version: Download Gmail from Google Play)
2. Tap the Email you want to manage
3. Tap menu button and choose "Change Labels"
4. Here you can see the current labels for the specific email. Mark or Unmark the labels and hit "OK"