If you wish to leave a message for someone, sign into your profile, locate the person you wish to leave a message. Click on that members username or photo and go on their 'wall'. Type in your message in the field below 'Say hi to (name of person). Click 'post update' when you are done.
To check that you successfully left a message for that particular person, go to 'Activity' by clicking on 'Activity' at the top of the page. If your screen is small you will have to click on the 3 horizontal lines to be able to select 'Activity. Your message will appear with an arrow that looks like ( => ).