Help me out with this Gengar damage calcs

Ok I really suck at damage calcs and barely even have the slightest idea to do it so help me out here. So if a modest max SpAtk Gengar(394SpAtk) with NO boosting items like life orb and choice specs doing the following attacks to the following pokemon, tell me the damage calcs for it.

1)Giga drain on a Max HP Swampert, no special defense investments
2)Icy wind on Salamence with no HP investment, and no special defense investment
3)Icy wind on Dragonite with no HP investment, and no special defense investment
4)Icy wind on Gliscor with max HP, and no special defense investment

Also if you can, explain to me how the damage calcs work so I can figure it out next time.

^