I want to know what parts of speech is the word "is".
The word is is the present-tense third-person singular form of the verb to be.
1st person present: I am we are
" " past: I was we were
2nd person present: you are
" " past: you were
(note: English does not have 2nd person plural)
3rd person present: he/she/it is they are
" " past: he/she/it was they were