We use the apostrophe to form contractions and to show ownership. The mark is used to create plural forms only when using s to form a plural would be confusing.
In They're finishing the project, the apostrophe indicates that you've left out the a in are. In She said she'd catch the next flight, the apostrophe indicates the omission of woul in would. Many people consider contractions to be informal—appropriate to spoken but not to written English—but they often have a place in day-to-day workplace writing. They don't belong in rules, regulations, directives, and contracts, but they can help create a conversational tone in correspondence. Contractions are especially important in plain language texts of all sorts. Use them when the occasion calls for a relaxed or personal tone. I'm looking forward to meeting youis arguably better for business than Making your acquaintance is eagerly anticipated by the undersigned.
When you write Sam's boots, you're indicating that the boots belong to Sam. Here, the apostrophe indicates the omission of h and i. Sam's