The R/S Calc takes information you put in (eg. pokemon, gender, trainer data, ribbons, EV, PP, moves, level, exp,...) and makes a Hex code formatted for different cheat devices such as Action Replay, GameShark and CodeBreaker. Simply input the stats you want your pokemon to have, then click the 'generate' button. A code will appear on the right side of the screen. You can either type that in manually into the device, or click the 'create file' button (name might be different) and make the code into a file that you can open using the ARGBX program or the GameShark equivilent.
Note that you need to choose the Box and Slot that you want the pokemon to appear in. Make sure that that slot is empty, else the existing pokemon will be deleted. Also, as long as the code is on, moving the pokemon out of the slot it was spawned in will result in a copy being made. To avoid this, make sure to turn the device off before moving the pokemon. Also (again) you probably don't know your 'Secret ID'. If the Secret ID of the pokemon and that of the game don't match, then the pokemon won't be considered 'yours' and thus you can't change its name. Also (3X) The PokeDEX won't be updated with the pokemon cheat. You need to generate a PokeDEX cheat or spawn the pokemon in one cart and trade to the cart you want them in.
Hope this helps.
~EX