To understand any language, including Japanese, you need to know verbs — the words that convey action. Like English verbs, Japanese verbs have a few eccentricities, so you need to keep a few facts in mind when you're dealing with Japanese verbs:
Habitual actions and future actions use the same verb form, so taberu means I eat and I will eat. (You can think of it as the Japanese equivalent of present tense.)
You don't conjugate according to person. It doesn't matter who's eating — you use taberu for I eat, you eat, he/she/it eats, We eat, and they eat.
Use the stem form if you're adding a suffix to show politeness or another condition.
Use the te-form if you're adding another verb or an auxiliary verb to the main verb.
In Japanese, you don't conjugate verbs according to person; rather, you use different forms for present and past tenses, for affirmative and negative statements, for polite and informal speech, and to convey respect. The following table shows the various forms of taberu (to eat).

Language Phrases Glossary
accusative case
When noun or pronoun is the direct object of the verb of the sentence, you are required to switch to the accusative case ending.

Language Phrases Glossary
dative case
When noun or pronoun is the indirect object of the verb of the sentence, you are required to switch to the dative case ending.

Language Phrases Glossary
genitive case
When the noun or pronoun indicates possession, you are required switch to the genitive case ending.

Language Phrases Glossary
instrumental case
A Russian grammatical term that indicates that the noun or pronoun assist in the carrying out of an action, you are required to switch to the accusative case ending.

Language Phrases Glossary
interrogative
Words used to ask questions, such as who, what, when, where, and why.

Language Phrases Glossary
macron
A small, horizontal mark above the vowel that indicates a long vowel sound. Make the vowel sound like its name.

Language Phrases Glossary
nominative case
When noun or pronoun is the subject of the sentence, you are required to switch to the nominative case ending.

Language Phrases Glossary
prepositional case
A grammatical case that indicates that the noun or pronoun is the object of a preposition, you are required to switch to the accusative case ending. Used with the Russian prepositions: v (v; in), na (nah; on), o (oh; about), and ob (ohb; about).