If you particularly enjoy -- or dislike -- the links or comments posted by another Reddit user, you may want to send that person a private message. You can send such a PM by clicking on any Redditor's username and selecting "Send a message."
Sending and Receiving Private Messages
To send a private message to another Reddit user, just click her username and select "Send message." Fill in the contact form and click on the "Send" button to send your PM.
Conversely, if you want to read the private messages you have received, click on the "Inbox" icon next to your username and select "messages" to filter out comment and post replies.
Limitations of Private Messages
Reddit does not allow its users to send or receive attached files via private messaging. If you want to send an image or document along with your PM, your only option is to upload the file to a third-party host and add a link to the uploaded file in the body of your private message. Typical third-party hosts include Imgur and Tinypic for images and Google Drive or Microsoft OneDrive for documents.