You can message other Quora users using our 'Messages' feature.
On web - click on your profile icon in the upper-right, then click on 'Messages'. In order to send a new message, click on the 'New Message' button in the bottom-right
On our mobile app - tap on your profile icon in the upper-left, then tap on 'Messages'. In order to send a new message, tap on the message bubble icon located in the bottom-right.
You can also message a user directly by visiting their profile, clicking on the 'more' menu below their name & bio (e.g., the "..."), then clicking the 'Message' link in the drop-down menu.
You can control who sends you messages on Quora, and you may not be able to message all users on Quora (depending on their settings). The default mode for messaging is that, with some exceptions, you will only receive messages from people you follow on Quora. You can allow anyone to message you by changing your privacy settings. You can also choose to turn off messages altogether.