Making the choice between 'People are' or 'Is' sometimes causes confusion but the explanation is quite simple.
There is also sometimes confusion over the difference between people and peoples, and person and persons.
People or Peoples
People is the plural of person.
As it is treated as a plural noun it takes the plural of the verb 'to be' (are/were) and the plural of any other type verb.
Many people are going to the concert
People are often afraid of noises at night
Three people were in the shop
It is the case, however, that people is sometimes used as a countable noun, meaning that it can be seen as singular or plural with an 's', i.e. peoples.
This is when it is used to refer to a whole group of people such as a nation, tribe, country or ethnic group, referring to them as one unit.
But often it is not being used as the subject of the sentence and thus with a verb. Rather it is being used as what is called the predicative nominative, which means it is renaming the subject.
And if it is used as the subject, it still takes a plural verb, as countable nouns always do:
Christianity as a religion is found amongst many peoples of the world (aspredicative nominative)
The native peoples of Australia are the Aboriginals (as subject)
Person or Persons
If we wish to use the singular, 'person', then we use 'is / was'. This is of course to talk about one person.
Only one person is allowed in at a time
He is a person who likes music
We do sometimes also use persons instead of people. This is when we are using it perhaps in an official way such as on some instructions or in a legal sense
6 persons maximum in the elevator (instructions)
Persons wishing to apply for a visa must meet several requirements (legal)
Tip for People are or Is Grammar
If you are learning English for normal usage and general writing, then it is unlikely you will be using the singular people or using persons in a legal sense. So you just have to remember that people takes a plural verb.
People are / were...
Person takes the singular:
One person is / was...
It would also only be in very specific and quite rare circumstances that you would need or wish to use peoples, and even then it would be optional and you could use people instead.