As I said, server-side traces (just like Profiler) lets you see when various things happen in SQL (stored procedure begins, stored procedure ends, login succeeds, login fails, etc)

Traceflags change the behaviour of the SQL engine (eg if traceflag 1222 is enabled, information on deadlocks is written to the SQL error log. )

There are lots of documented traceflags, there are lots of undocumented traceflags, I don't know if there's a comprehensive list anywhere. Some are in books Online. Start there.