Below are the steps which you can follow to start Selenium:-
There are multiple programming languages supported by Selenium.
You can go through all supported language and choose one of it.
You can use core Java, then explore core Java and lean it, be able to code core Java code
You need to learn the testing framework with Java, TestNG is one of it… explore it as well.
You should have basic knowledge of build tool if working with Java to go for maven.
You must learn about web technology and create locator.
Need to explore XPath tutorials.
Browser Automation is the site you can refer once you are done with point 1 to 7
If you want to learn more about Selenium you must have a look at the following Selenium Training Course. I am also mentioning a video tutorial which you must watch to learn all about Selenium.