The best way to learn SQL is to use it. Find a tutorial online or buy a book (such as "SQL for Dummies") and work through the examples. Pay attention to the syntax and try to understand what each statement is doing. If you get stuck, ask a question on a forum or search for an answer online.
In addition to practicing SQL, you can also read articles or watch videos about it. This will help you to understand the concepts behind the syntax. Once you understand the concepts, it will be easier to write SQL statements on your own.