If you are running your machine on ubuntu, taking screenshot is very easy and fun. There are few ways to do it and you can choose any which suit you.
1. Using panel tool
Navigate to your home > Accessories > Take Screenshot
2. Using Shortcut
Hold print screen button (prt sc) or maybe sometime you need to hold with fn key . eg fn + printscreen
3. Using Gimp (my favourite way)
Im not sure GIMP under Windows and Mac having the same features or not. But i like taking screenshot directly with GIMP because it automaticall paste your image into editor and you can edit after that if you want.
The best thing taking screenshot with ubuntu is you also can set timing (timer) before it start screenshot.