Knave said:
Today is Monday - 今日は月曜日です。 kyou wa getsuyoubi desu.
Yesterday was Sunday - 昨日は日曜日でした。 kinou wa nichiyoubi deshita.
Tomorrow is Tuesday - 明日は火曜日です。 ashita wa kayoubi desu.
Correct!
Knave said:
Also, please help me with the different forms of the copula. I've read many charts and things, but they give me soooo many different ways of saying it. Please tell me what is mostly used by adults, teenagers, or whatever it may be.
Present Tense
Plain - だ da では dewa or じゃない ja nai?
Polite - です desu では dewa or じゃありません ja arimasen?
Please also tell me what the past, future, and tentative forms of the copula are.
That's not really present tense. It's more commonly and accurately called "nonpast." Japanese verbs,
like English verbs,
don't have future tense. Moreover, Japanese doesn't have a modal verb to show future tense.
Anyway, here you go:
Nonpast plain - だ, である (formal written language)
Nonpast formal - です, であります (more formal, often used for speeches of politicians, et al)
Nonpast negative plain - では (じゃ) ない
Nonpast negative formal - では (じゃ) ありません
Nonpast negative colloquial formal - では (じゃ) ないです
Note that じゃ is the contraction of では.
Past plain - だった, であった
Past formal - でした, でありました
Past negative plain - ではなかった
Past negative formal - ではありませんでした
Past negative colloquial formal - ではなかったです
Plain conjectural ("probably") - だろう
Formal conjectural - でしょう
If you learn some verb and adjective inflections then getting things like であれば and じゃなかったら shouldn't be a problem, because you can see that ある is a verb and ない is an adjective. I would suggest reading through the Teach Yourself Japanese site (link in my sig) and searching for verb and adjective conjugations or inflections to get a better understanding of the processes at work here.