Archiving conversations is a great way to organize your inbox. It allows you to move old and unwanted conversations to a new tab, so you can keep your main inbox dedicated to conversations you intend to follow up with.
To archive, a conversation, navigate to your inbox and select the conversation you wish to move. Once the conversation is open, select the little box in the top right corner of the conversation window. The conversation will automatically be removed from your main inbox to your Archived tab.
Have you changed your mind or archived a message by mistake, do not fret! See How do I unarchive a conversation?