Some basic rules for using apostrophes in English grammar include:
Use an apostrophe to show possession.
Use 's to indicate possession with singular nouns, and s' to indicate possession with plural nouns that end in "s."
Use an apostrophe after the "s" to show possession with plural nouns that do not end in "s," and before the "s" to show possession with plural nouns that end in "s."
Do not use an apostrophe to make a noun plural.
Use an apostrophe in contractions to indicate missing letters. For example, "it's" instead of "it is."