You can post to your wall in the Profile tool by entering a status message, or by posting directly to your wall.
Go to Profile.
Select the Profile tool from the Tool Menu in your Home area.
Enter a status message.
Enter your message into the text box provided and then click the Say It button.
Note: Status messages are limited to 140 characters. You will see a counter to the right of the text box that tells you how many characters you have remaining.