You can type letters or numbers (including spaces) into the Youtube search field using the on-screen keypad. Navigate to the "search field" box for the Youtube application and press the center button (ENTER) on the supplied remote. Refer to the following link regarding how to enter letters or numbers in the search field box using the on-screen keypad.
You may also connect a 101 keyboard to the USB jack of the Blu-ray Disc player for manual text input, like entering a web address or url and performing web searches. However, the keyboard cannot be used to control BD player functions such as playing a disc and menu selections.