Sometimes people put apostrophes into words that end with s. For example, often writers add apostrophes to plural words that are not possessive. The bug's sing and dance on the lawn. Just because a word ends with an s does not mean it needs an apostrophe. Make sure that you only use apostrophes to show possession and in contractions.
Some words always cause apostrophe trouble.
This group includes his, hers, its, and theirs. It is important to check your apostrophes before turning in a paper. It's , with the apostrophe, is a contraction. If you can use it is , then it's is the right choice. Who's , with an apostrophe, means who is.