From my reading of posts here and elsewhere, Scratch is not yet "ready for primetime."
Use the Arduino IDE to program the littleBits Arduino bit. The latest IDE (1.8.1) has a setting (Tools > Board > littleBits w6 Arduino Module (Leonardo) ) specifically for the littleBits arduino bit, but if you have an earlier version, just use the Leonardo board, and it'll work just fine.
Remember that D1, D5 and D9 are the outputs, and D0, A0, and A2 are the inputs available with the littleBits arduino module. You can change these with your sketch of course, but I like to keep to the littleBits protocol of inputs on the left, outputs on the right.
Start with the Blink.ino sketch. It won't run as published in Examples >Basics > Blink because there is no LED attached to pin 13, as there is in most boards manufactured by Arduino. Change references to pin 13 to pin 9 and it'll work just fine when you put an LED bit on the bottom right bitSnap. Then go from there.
Post back on the forum if you run into issues going forward. Post back in this thread if you have trouble with this. I'll monitor the thread and pop in if you need any help.