The DigiSpark is small and inexpensive. To keep it that way it has limited features. One feature that Arduino programmers may miss is the monitor terminal window. On the Arduino this is used to send and receive information from the Arduino.
Although the DigiSpark does not suppor the monitor window there are several options available with similar features.
* The simplest is the DigiKeyboard.println. You can use this where you would use serial.print with an Arduino. To use this you will need to add the keyboard library.
* As far as DigiUSB tools packaged with the software I think the DigiUSB library (see the Echo example for how to print a message back to the computer) in conjunction with the digiusb.exe program in the DigiUSB Programs folder is the simplest option - use the library in your sketch, print out the data you want to see on the computer (like using Serial with the Arduino) and open digiusb.exe once you're device is plugged in - it then should display similar to the Arduino serial monitor, showing messages as they come in and allowing you to send data to the device (if you've set your sketch up to receive it). If you give that a try and have more questions let me know and I'll be sure to answer them tomorrow.
* The Rubygem is a great tool also