Microsoft put an amazing (IMHO) poster online which provides you with a visual reference in order to understand key technologies in Windows Server 2008 R2. Focus areas are:
- Active Directory Domain Services
- Hyper-V
- File Services
- Internet Information Services
- Remote Desktop Services
- BranchCache
- Direct Access
- Management
So my advice, download the poster and print it out (in color) on a large size paper and hang it on your wall in your office.