Doodle Message have no more setting to configure. Once installed, all you need to do is just press the small Camera icon in Messaging screen. Note that, you may not always be able to send doodles to other types of phones.
The doodle you create, is send as standard image file, which means, the other user does not require to have Doodle Message or any other add-on installed on his/her phone.
Doodle Message is a free tweak and you can download it on Cydia via Bigboss repo. Its fun when you can draw your freehand drawing!!