The centerpiece of that summary is a quote from the beginning of a detailed analysis by Paul Lukasiak. I'll give you the key sentence.
An examination of the Bush military files within the context of US Statutory Law, Department of Defense regulations, and Air Force policies and procedures of that era lead to a single conclusion: George W. Bush was considered a deserter by the United States Air Force.In brief: Bush skipped out, and pulled strings to avoid the consequences. Since then, there's been extensive tampering with records to cover it up.
Update! Brad DeLong offers the helpful long summary that I didn't have time to prepare.