How do you insert a script (Not into the main stuff but more confuding)

ok i found a realy cool battle system but i dun understand these instructions

This script is a simple script to implement side-view battles. Modification is required if you want the characters to walk up to the monsters and attack, for instance. The first block of code below should replace Game_Actor#Screen_X. The second block should replace Game_Actor#Screen_Y. The last block should replace Window_BattleStatus#Update. If you want to change the arrangement of the party members on the battle screen, play around with the return values of Game_Actor#Screen_X and Game_Actor#Screen_Y until you find something you like. Please note that the coordinates provided in this script are intended to be used with battler images the size of map sprites. If you keep the full-size battler sprites, this script will make your battles look really stupid.

please help ^^

Well, when it says "Game_Actor#Screen_X" go to the script titled "Game Actor" or "Game_Actor" I forgot. Anyways, then go down to wherever it says "def Screen_X" (I think) then replace the codes. I think this is how it's done.

thanks^^