Exchange Server 2010 is the server side of Microsoft's client-server e-mail product. The client side is usually Outlook, although it can also be accessed in other ways such as via a web browser, or using mobile devices. Web browser access, known as Outlook Web Access, is almost as full-featured as Outlook itself, with the major exception being the ability to work off-line.
This version of Exchange is 64-bit, and thus, runs only on 64-bit operating systems. Exchange 2010, along with Exchange 2007 before it, was designed with server consolidation in mind. Due to these design changes, "Hosted Exchange" has become very popular with small organizations as performance is extremely good even though the server is being accessed over the Internet. This allows small organizations the features of Exchange without having to manage and maintain a server. Despite Hosted Exchange's popularity with small organizations, many large organizations have also outsourced this functionality.
Questions about configuring Exchange 2010 Servers are more appropriate for Server Fault.