There's a lot of information out there that will help you plan, design and manage your high availability or site resilience solution. For example, you might want to start with this four-part video blogcast on high availability in Exchange 2010:
Next, visit the Exchange 2010 library in TechNet, where you can read topics that will help you understand high availability and site resilience in Exchange 2010. When you're ready, check out these TechEd presentations for deeper technical content:
To read all available library content for Exchange 2010 high availability and site resilience, see High Availability and Site Resilience in Exchange 2010.