Fast Startups allows you to boot around 70% faster then you normally could. Windows does this by utilising the hiberfile.sys but thats all too technical, if you interested in that then read this post on the Microsoft MSDN Blogs http://blogs.msdn.com/b/b8/archive/2011/09/08/delivering-fast-boot-times-in-windows-8.aspx
Getting to the Power Options
1. Open Start and type Power Options then choose Power Options. (or press the Windows + X key and choose Power Options)
2. Then click Choose what the Power buttons do
3. Then click Change settings that are currently unavailable
4. Now scroll down and check the box “Turn on fast start-up (recommended)”
Fast Start-up is now enabled, if you ever wish to disable it then repeat the steps and just uncheck the box at step 4.