Focalin is a stimulant and its active ingredient dexmethylphenidate is a sort of "refined" version of the methylphenidate used in Ritalin, Concerta, etc.

The effects/side effects are pretty similar to those of other amphtamine-based stimulants used for treating ADD.

No, Focalin doesn't do anything that Ritalin doesn't do. Methylphenidate is a chemical compound and those parts of this compound that don't really do anything are removed leaving just the active d-isomer of methylphenidate, which is then called dexmethylphenidate.

Since Focalin is a sort of concentrated version of Ritalin the dose is usually about half that of Ritalin. There is really not much difference between the two apart from the dose needed to achieve the same effect.