1. Put their name in the first chat box (case sensitive)
2. Select the "Whisper" option where you now see "Talk"
3. Then, type your message in the second chat box
my char name is JozeF
Hope to see you in game
EDIT: Hey I saw where you tried to whisper. I must have been afk at the training ground. I saved your char name so I will try to whisper you when I'm on as well.