When you type a quote or apostrophe symbol on your Mac, it will usually automatically convert to the curly version. However, you can control when this happens on a per-app basis. You can also make exceptions to the process while typing. See examples in TextEdit, Pages and Mail.
Grammar mistakes can be pointed out to you in apps such as TextEdit, Mail, Pages and Microsoft Word. However, grammar checking is very difficult for computers and only some mistakes can be spotted. Use grammar checking as a second level of spell checking and a way to avoid typos. But do not rely on it to actually fix bad grammar.
Tab stops allow you to align text in word processing programs. They have been around for a while, but if you have only started using word processors recently, you may have overlooked them in favor of tables and other layout elements. Tab stops are a quick and easy way to display data neatly inside a document.