I would like to note a user but I do not know how. Can you help me?

You can do this one of two ways;

1.) The first is by visiting the userpage of the person you wish to note. Once on their userpage located to the right of user stats will be a link entitled 'Send a Note', clicking this will allow you to note the user.

2.) The second method is to visit the "Notes" section of your 'Message Centre', by clicking on your messages link followed by the "Notes" tab.

Please be advised you must be logged in to your account or have a deviantART account to make use of the notes system.