How I can learn selenium automation.

There is no need to attend selenium classes. Most of the automation tools are available online including selenium.You can find ample of tutorial and video on internet with the help of which you can learn selenium at your ease.

For Selenium web-driver you need to learn basics of Java. Basic knowledge of java covers below topic

• Variable, Data Types, String
• Conditions and loops
• Array and Functions
• OOPS Concepts
• Collection(List, Hashmap etc)

Below are some reference link where you can start learning Java

• Java Tutorial - javatpoint
• Java Tutorial - Learn Core & Advanced Java Program
• Trail: Learning the Java Language
• Java Tutorial - Learn Core & Advanced Java Program

Also there are various free video tutorial which are totally free. I am giving some link

• Learn Java: Free Java Programming Tutorial For Beginners
• Java for Humans: Introduction to Programming - Udemy
• Java Basics: Learn to Code the Right Way - Udemy

Once you are done with learning basic Java concepts , you can start learning Selenium. There are number of free selenium tutorials which are available in market explained by professionals .I am adding some here.

• Top Selenium WebDriver Training with Java - Basics
• Getting Started With Test Automation Using Selenium

Popular tool available for test automation

Generally there are two types of automation tool available in market.first is open source, which are easily available on internet .Second one is licenced for which you need to spend money.

I you are looking for web automation then below tools are best for this purpose.

1. Selenium is very popular tool ,which is open source. you should have basic knowledge of any of the six programming language(Java,C#,JavaScript,Python,PHP,Ruby) which selenium supports.selenium do not support windows automation.
2. HP’s UFT is another tool which can be used for web automation as well as for window application. To write script in UFT tool you should know the basics of Vb-script language.
3. Other tools which are used for web automation are test-complete, SOAPUI etc.

for mobile automation below tools are popular-

1. Appium is most used toll for mobile automation. It supports automation for both IOS ,Android application. Appium support six programming language(Java,C#,JavaScript,Python,PHP,Ruby).
2. Robotium, Espresso(Supports only Android), XCTest(supports only IOS), Perfecto(Support both IOS and Android application) are other tools used for mobile automation.

for learning basic of java please check below answer

Which Java concepts I should focus on?