Install the Arduino IDE
First step to use the ATTiny Digispark USB board is to install the Arduino IDE. You can find the procedure on the Arduino/Genuino website, available for all the OS: https://www.arduino.cc/en/Main/Software
Digispark tutorial
The Digispark board comes with a dedicated provider wiki page so you can play around !
http://digistump.com/wiki/digispark/tutorials/connecting
You can flash the digispark example DigiBlink as suggested. The example codes are under /File/Examples/Digispark_Examples Do not forget to set your board to Digispark default (16.5MHz) before upload.
In case you get a compilaiton error with one of the examples, just reinstall or update the AVR device manager as indicated here: