It's possible to apply more than one label at a time, as well as create sub-labels. When you Label an e-mail, you are simply adding an identifying tag. When you Move an email, you are filing it away into a folder. To create a label, you can either go to Settings > Labels > Create New Label, or when you have an email open, you can click the 'Move to' or 'Label' icons, then hit 'Create New'. Labels can act as folders – places to store messages instead of the inbox – or they can act just like regular labels, identifying tags that appear next to the subject line of your messages to help keep you organized. If you're not using labels in Gmail, it's time to start. Here are New Atlas' tips for achieving an immaculate inbox so you can find what you need, when you need it. However, it's easy to abuse those luxuries and find yourself buried in an inbox thousands of messages deep.
Ample storage space and extreme searchability are two of the driving factors behind Gmail's popularity.