If you want to become an expert in Selenium you can easily become because Selenium is easy to learn, it is fun and free to learn and practice, provided you must know about coding. Moreover, it is in-demand.
You must go through with the following Selenium Tutorial to learn Selenium in a better way. When I started my career in software testing with Selenium I was put into manual initially but without wasting much time I learned Selenium. Again selenium like most of the technologies is something that you need to practice a lot.
You will find numerous times where you will get stuck onto something for long. Do not back out keep trying, this is what will give you experience and confidence.
Lastly, if you have no knowledge of coding. Learn and practice a programming language like core Java or Python first. You must take up the following Selenium Training Course which will definitely make you expert in Selenium.