In the English language, you form a plural by putting a "s" after the word, unless the word ends in an "s", in which case you use "ses". So, one car -> many cars, one bus -> many busses (note the double s). There are a few irregular nouns but they all come from other languages (thus one crisis -> many crises, because crisis is Greek).

You never use an apostrophe when forming a plural. Using an apostrophe forms the possessive.