You use the past participle and the present tense of the verb to be, except that the verb to be is always dropped in the third person. The past participle should agree with the subject in gender and number, because grammatically it's an adjective. So "I cooked" is "Vařil jsem" or "Vařila jsem", depending on the gender of the speaker. "You cooked", singular informal, is "Vařil jsi" or "Vařila jsi", depending on the gender of the listener/reader. "He cooked" and "She cooked" are "Vařil" and "Vařila" respectively. "We cooked" is "Vařili jsme" or "Vařily jsme". The latter is used by an all female group and the former otherwise. "You cooked", plural, is "Vařili jste" or "Vařily jste", depending on the gender of the listeners/readers. "You cooked", formal singular, is a bit weird. Czech uses the plural form of the verb to be, but doesn't pluralise the past participle, so it's "Vařil jste" or "Vařila jste". "They cooked" is normally "Vařili" or "Vařily". It could sometimes be "Vǎrila", which is the neuter plural ending, if the antecedent of the pronoun "they" is neuter. That might seem impossible, because inanimate objects don't cook, but it's (mostly) the grammatical gender which is decisive and some words which describe people are grammatically neuter. "Děvče", one of the words for "girl", is an example. Technically the same thing could happen in the singular, but in practice everyone ignores that rule in the singular. With any of these forms you can use pronouns, but unlike English you aren't required to. Using a pronoun will usually change the word order, because Czech is weird like that. So "I cooked" can also by "Já jsem vařil" or "Já jsem vařila". Some people drop the form of the word to be when they use a pronoun, as in "Já vařil" or "Já vařila", but this is simply confusing and, according to the grammatical authorities, wrong.
I'm not clear on how past participle is formed. I think I understand how to do it according to gender, but how would it be written according to which class of verbs it's in? (like if it's in the first class of verbs, how do I change the verb, and the same with the other three classes) I hope I worded that well.
You worded it fine, but I don't know what the three classes are. Normally Czechs don't refer to them in grammatical discussions, but just give a representative example. If you give me a list of verbs I can give you the past participles. For simplicity I'll just give the masculine singular form, since the pattern for forming the others from that is always the same.
Jak se vyjadřuje dokonavý a nedokonavý vid slovesa v angličtině? Já bych "My wife cooked rice" přeložil spíš jako "Moje žena UVAŘILA rýži". A větu "Moje žena VAŘILA rýži" bych přeložil naopak jako "My wife was cooking rice".
Ano, mate pravdu. Casto se to takto rozeznat da. Ne vzdy. Nekdy je to jasne jako facka a nekdy se ta dokonavost moc obejit neda. Tady uznavame jak varila, tak uvarila. Moje zena k tomu kureti vcera varila ryzi. Ale i v CJ tady muze byt uvarila ryzi. A vyznam bude stejny. Mel jste k veceri ryzi. V aj je to, v teto vete, stejne. Pokud nepotrebujete z nejakeho duvodu zduraznit dokonavost ci nedokonavost te cinnosti, tak vam projde oboji.