Information can be mostly found in the Monster Manuals.
Basically, they add extra stuff such as resistances and attacks.
Lets take the Half-Dragon as example (dunno if its in):
No change in size, hit dice increases 1 step (doesn't apply to class hit dice, only racial hit dice), large and larger half-dragons gain wings and a fly speed of twice its base land speed (max 120ft), medium and small doesn't, +4 natural armour class, two claw (primary) and 1 bite attack, a breath attack, darkvision (60ft), low-light vision, immunity to sleep and paralysis, immunity to damage type (based on colour), +8 Str, +2 con, +2 int, +2 cha, gains skill points as a dragon for its racial hit dice, gains the alignment of the dragon they're half- of, and a +3 Level Adjustment.
Or at least, that's how the PnP version has it.
I don't really know how they've implemented it into NWN.