In Japanese there is something called short form. It's called this because it is literally shorter than the "polite" verb conjugations in Japanese.
Short form is used a lot in casual conversation. BUT! Short form ≠ Casual. Just because something is short form it doesn't mean it's casual. There are a TON of different verb forms that require short form. Progressive form uses short form; whenever you say something like "X said ______" or "I think ______" you use a short form verb; listing actions uses short form; connecting verbs uses short form, and there are many other situations where you use short form.
Therefore I felt you should learn short form early in your Japanese-study-career because it'll help a lot with other grammar points to come.
The first thing about short form I'll cover is the short form of verbs. The short form of adjectives will be covered later.
The plain short form of verbs (used for future/continual actions,) is just the dictionary form of the verb (the form you find when you look up a verb in the dictionary.)
The plain short form of verbs (used for future/continual actions,) is just the dictionary form of the verb (the form you find when you look up a verb in the dictionary.)
So the short version of: にほん に いきます! is just にほん に いく!
The plain short version on the auxilllary です is just だ.
すし だ = It's sushi.
Next in the list of short form verbs is the て and た form. This set is the hardest verb conjugation in Japanese (don't be scared though! It just takes a little more memorization than other conjugations.) て form and た form (aka short past form or short form past) are very similar. So once you know one you can easily learn the other.
The ending of the verb determines the change. Here is a table:
て FORM
FOR GODAN VERBS
う、る and つ ・ ・ ・ become ・ ・ ・ って ➔ example: うつ becomes うって
く ・ ・ ・ ・ ・ ・ ・ becomes ・ ・ ・ いて ➔ example: かく becomes かいて
ぐ ・ ・ ・ ・ ・ ・ ・ becomes ・ ・ ・ いで ➔ example: かぐ becomes かいで
ぶ、む、and ぬ ・ ・ become ・ ・ ・ んで ➔ example: とぶ becomes とんで
す ・ ・ ・ ・ ・ ・ ・ becomes ・ ・ ・して ➔example: かす becomes かして
FOR ICHIDAN VERBS
Drop the る and add て ➔ example: たべる becomes たべて
た form is super easy. Just take the above conjugations and replace て with た and で with だ.
So はなす becomes はなした, およぐ becomes およいだ. And so on.
Using て and た Form
た form (usually) is the short past tense form of the verb.
もう たべた。 = I already ate.
ともだち と いっぱい はなした! = I talked with my friends a lot!
かれ は もう かえった か? = Did he already go home?
もう たべた? = Have you eaten?
If you'll notice from the last two examples, there is no past-perfect form in Japanese. So "I have already eaten" and "I already ate" translate to the same thing in Japanese.
The short form past tense of the auxiliary だ is だった.
て form has a wonderful variety of uses. One is progressive. If you add いる (informal) or います (formal) onto the end of a て form verb then it becomes progressive.
はなして います = Talking
あそんで いる = Hanging out (lit: playing)
Probably one of the most important usages of the て form is commanding. If you want someone to do something, you use てform.
きて、きて! = Come on! Come on! (calling someone to join you, etc.)
ちゃんと いって! = Just say it!
ちゃんと いって! = Just say it!
If you would like to be less forceful and more polite then you add ください (please) to the end of the verb.
すわって ください = Please sit down.
なまえ を かいて ください = Please write your name.
Another usage of て form is connecting verbs.
けさ、あさごはん を たべて、がっこう に いきました。 = This morning I ate breakfast and went to school.
In this above sentence there are two verbs, "eat" and "go to school." In English if you connect to verbs then both verbs are in the same tense, (like ate and went are both past,) and then use "and" to connect them. In Japanese, you make the first verb (s) て form and then the final verb changes to past, future, whatever. Here is another example:
おんがく を きいて、ほん を よんで、かいもの に いく! = I'll listen to music, read a book, and go shopping!
て form is not the only way to connect verbs, (there are two more ways,) but it is used often especially for making words like "come back" or "bring with."
To come back = かえって くる = かえる (return) in て form + くる (come)
To go back = かえって いく = かえる (return) in て form + いく (go)
To bring = もって くる = もつ (to hold/have) in て form + くる (come)
To take = もって いく = もつ (to hold/have) in て form + いく (go)
There are many other ways in which て form and た form are used in conjunction with other conjugations (for example, one of the other ways to connect verbs includes た form + another suffix,) but those will be introduced in later lessons.
For now just work on memorizing the て form table above maybe with flash cards or making a table of your own.
Good luck!!
がんばって!!