Lesson 1: State of being with だ and です
Japanese has two basic "is" words. The grammar term for "is" words is "copula". Copulas have a dedicated term because they're special.
The two copulas in japanese are だ and です. です is more polite than だ. Despite both being copulas, they can't always be used in the same patterns.
Unlike english, the state-of-being word goes after the word that you're using to describe something, rather than before it.
ペンだ
It's a pen.
ネコです
It is a cat.
The difference between だ and です is sometimes translated as a difference in whether a contraction is used, but this is not what's happening in japanese.
Later on, we'll see です get used in places that english wouldn't allow "is". It can act like a filler word instead of a copula.
Japanese has two basic tenses: the simple tense and the simple past tense. Dictionaries list verbs by their simple tense. We're only using the word "simple" to say that nothing else is added to the verb.
The simple past form of だ is だった. The simple past form of です is でした.
オレだった！
It was me!
そうでした
That was so.
The simple tense is usually called the present tense or the non-past tense. It's important to remember that it can be used in a lot of situations. Present tense and non-past tense are reasonable names, but don't treat names like rules, sometimes names are confusing. We'll be using these names interchangeably.
The simple tense and simple past tense usually line up with english's present and past tenses, but they're not used in all the same places. Just remember that english and japanese use tense in different ways.
In japanese, ordinary statements about the future use the simple tense most of the time. This is where the name "non-past" comes from.
The simple past tense is usually just called the past tense. Sometimes it can also be used for things that already completed like "has become", even if they're hypothetical and haven't happened yet.