eigentlich ist das ganz einfach;) also... does benutzt man bei he/she/it also zb. she does, he does.... / she doesn't he doesn't

do bei den anderen formen also zb. i do, you do, we do, you do, they do, wobei don't einfach die verneinung ist also... i don't usw.

und did/didn't ist die vergangenheitsform, allerdings für alle "personen":

i didn't do that, you didn't do that, he/she/it didn't do that...