~masu (～ます) - it is used for verb but it is formal. Also, it is present or future tense. Here are few examples:
To Eat - Taberu たべる：
Taberu is Ru-verb. You have to remove ru then add masu at end as tabemasu たべます.
To say - iu いう：
iu is u-verb. You have to replace 2nd u for i then add masu as iimasu いいます.
To drink - nomu のむ：
nomu is u-verb. You have to replace u for i at end then add masu as nomi のみ.
To study - benkyousuru べんきょうする：
benkyousuruis irreglaur verb. You have to remove suru at end then add shi then masu as benkyoushimasu べんきょうします.
~desu (~です) - it means "am/is/are/will". Also, it is formal. For example, nihonjin desu にほんじんです. It means "I am Japanese."
~desh*ta (~でした) - it means "was/were". Also, it is formal. For example, nihonjin desh*ta にほんでした. It means "I was Japanese."
arimasen (ありません) This word has 2 meaning. First, it is negative for noun and adjective. And it is formal.
ja arimasen is used for na-adjective and noun. For example, nihonjin にほんじんじゃありません. It means "I am not Japanese.
" Another example, kirei ja arimsen. きれいじゃありません。 It means "I am not beautiful." kirei is na-adjective as kireina but u remove na at end for ja arimsen.
onjugation rules for nouns/adjectives with「ありません／ありませんでした」 form
For nouns and na-adjectives: Append 「じゃ」 and then 「ありません」 for the negative or 「ありませんでした」 for the negative past.
Examples
•元気＋じゃ＋ありません ＝ 元気じゃありません
•きれい＋じゃ＋ありません ＝ きれいじゃありません
•元気＋じゃ＋ありませんでした ＝ 元気じゃありませんでした
•きれい＋じゃ＋ありませんでした ＝ きれいじゃありませんでした
Another term, it means "don't have" or "there is no (object)". For example, watashi ha okane ga arimsenわたしはおかねがありません。 It means "I dont have money."
imasu (います) - it means "I have/will have" or "there is/are/will" but it is used for person or animal. For example, are ha hito ga imasu あれはひとがいます。 It means "There is a person over there."
arimasu (あります) - it means "I have/will have" or "there is/are/will" but it is used for object. For example, watashi ha okane ga arimasu わたしはおかねがあります。 It means "I have money."
Note: arimasu and imasu are verb in formal. arimasu comes from aru. imasu comes from iru.