Click on Allow and Block specific programs to open the Application Restrictions window. The radio button at the top lets you specify if the account can Use All Programs, or Only Use The Programs I Allow.
If you select the Only Use The Programs I Allow radio button, the box below will populate with the applications that are instaled on the system and let you select the specific application or programs that the user account is allowed to use.
To block only certain programs, you can speed things up by selecting the Check All button at the bottom and then simply deselect the checkbox next to the programs or applications that you want to block.