There are a few ways to proofread on a Mac. One way is to use the built-in grammar and spell checker. To do this, open the document you want to proofread in Word, click the Review tab, and then click the Spelling & Grammar button. Word will then scan the document for any spelling or grammar errors and highlight them.
You can also use third-party proofreading tools. For example, Grammarly is a popular proofreading tool that can be used on a Mac (and other devices). To use Grammarly, you first need to sign up for an account and install the Grammarly plugin for Word. Once you've done that, you can activate the proofreading tool by clicking the Grammarly icon in the Word toolbar.
Another option is to use a free online proofreading tool like PaperRater. To use PaperRater, simply copy and paste your text into the PaperRater website and click the "Grade My Paper" button. PaperRater will then scan your document and highlight any spelling or grammar errors.