When you install Dynamics CRM (on-premise) or import an existing organization database, it performs a series of environmental checks to verify that you will not run into issues during the actual installation or import.
If you double-click on one of the warnings or errors it will open up a help file and show you details about the message. That file can be found here:
C:\Program Files\Microsoft Dynamics CRM\Tools\EnvironmentDiagnostics.chm
I found it quite interesting to read through the various details to see what is checked. That might help you to know some of those things before you actually begin the installation or import process.