Points of verbal conjugation

When "-masu/-desu" is used at the end of a sentence, the sentence considered as a polite style sentence.

"hayai, hayakunai, hayakatta, hayakunakattta"
"ii tenkida, ii tenki (dewa/ja)nai ,ii tenkidatta, ii tenki (dewa/ja) nakatta"
"iku, ikanai, itta, ikanakatta"
When these words are put on the end of a sentence, the sentences are called a plain style sentence (Futsuu tai).
In other words, the Futsuu tai is a sentence which ends by plain form.
 "-dearu" style also belongs to this style. On the other hand,

"hayaidesu, hayakunaidesu, hayakattadesu, hayakunakattadesu"
"ii tenkidesu, ii tenki (dewa/ja) arimasen, ii tenki deshita, ii tenki (dewa/ja) arimasenndeshita"
When these words are put on the end of a sentence, the sentences are called a polite style sentence (Teinei tai).
In other words, Teinei tai is a sentence which ends by polite form.

You can see 11 conjugational forms of verbs in the table bellow.
Each conjugation has a name like, nai-form, masu-form, dictionary-form and etc.

Do not cpnfuse a plain form and a plain style.
Watashi wa Chuugoku ni ittakotoga arimasu. (I have been to China). This sentence is a polite style sentence.
                                 * this part is a plain form
                                    The blue color words are all plain form when they are put before a word/phrase.

Most textbook introduces masu-form or dictionary-form first. That is quit understandable. However, It takes long time for
the master of all the verbal forms. Some of students feel stress since they can not express what they want to express "now".
If you can draw this table in your brain in early time, you will be aware of what you are studing "now".
And you will notice that Japanese verbal conjugation is not so difficult as a whole.  
Notice the oder of each form. Most textbook arrange each form according to the order of index.
You can see each form of the 1-groups verbs,
from left to right, ikanai, ikareru ,ikaseru, iki-masu, iku, ike, ikeba, ikeru, ikou, te-form ta-form..

When you want to express about your experience, you will make a sentence using the combination between ta-form and
"kotogaarimasu". When you talk about your intention, you will make a sentence using the combination between dictionary-form
and "tsumoridesu" or another combination between volitional form and "to omotteimasu". 

You can easily find the combination between some form of expression and an appropriatte conjugational form through this table.
So, JCC recommend you to make this table by yourself and make it use. If you make two types of table, that would be more
useful. One is the copy of this page, and another one is for your practice.
The more you study, the more the space of part B expands.

Table of verbal conjugation
 
G1: group 1
G2: group 2
G3: group 3

Note:
1. These expressions are very small part of all. Sometimes 2 different forms are in one expression, like "Kakebakakuhodo joozuni narimasu".
   (The more you write, the more you progress).
2. When you think about the word combination, you have to consider about;
   (1) which part of speech comes before the form of expression
       ex. 〜kawarini
           Instead of watching lots of video, why don't you go to a movie theater? (Ippai bideo o mirukawarini eigakan nidemo ittaradoudesuka).
           I came here on behalf of my sick father. (Byouki no chichi no kawarini watashi ga koko ni kimashita).
           This apple is cheep, but this is not tasty. (Kono ringo wa yasui kawarini oishikunai).

   (2) Appropriate inflection of adjectives and verbs
       ex.  〜tenaranai
           I can't help thinking so. (Sou omoetenaranai. Sou omowaretenaranai)
           I can't help being sad. (Watashi wa kanashikutenaranai)