Please help me to understand when and how to use is and are with a verb?
- Your letter is not yet come/came.
- Tree is fallen on him.
- Train is arrived.
- current is Gone
- He is died due to cancer.
Also, if I use has instead of is does it change the meaning?
As ultrasawblade said:
In the passive, the person or thing that the action was done to becomes the topic or theme. (CDO English Grammar Today)
This means that there has to be something/someone to whom the action was done, i.e. the verb should be transitive.
Come, fall, arrive and die are intransitive verbs, so your examples 1, 2, 3 and 5 are ungrammatical.
Your 4th sentence is different, because the verb to be is used as a copula (not an auxiliary to form the passive) so the meaning of the sentence is that the current is no longer present (it could make sense if you were talking of electric current).
On the other hand:
With have as an auxiliary all your sentences would be grammatical, although 4 might sound a bit strange.
See this question for an explanation why is + came is ungrammatical.
Almost every English verb can be used as an actual, real verb or take the form of a present or past participle. The present or past participle can be used as a modifier, or as an auxillary or helping verb.
English has various verb tenses and moods, and some tenses are expressed with one word, and others with more than one word - which is a form of to be + present or past participle, or a form of to have + past participle. It's best to think of the entire phrase (to be or to have + auxillary/helping verb) as the verb.
Progressive tenses use to be + present participle.
Passive moods use to be + past participle.
Perfect tenses use to have + past participle.
Each of these has a different meaning.
There are also modal auxillaries such as will, would, etc. that express future and conditional tenses.
Long story short: study your tenses!
