To respond to an employee or an employer who has reached out to you, simply log into your account and navigate to your inbox.
From there, locate the message(s) you want to reply to and click on the message to open the conversation window. Next, type your response in the text box and hit "send".
NOTE: It is very important to respond whether you are interested or not as it shows good etiquette. It also offers the sender closure so they can move on in their search and will not continue to reach out to you or wait for a response.