You can start learning Selenium by your own by reading the Selenium tutorials, or by watching Selenium videos. And for practicing Selenium you use,
Latest version of Selenium is Selenium 3, but try to use Selenium 2.23 for practice, Selenium 3+ version having so many issues.
1) Selenium WebDriver 2.23
2) Mozilla Firefox 12 version
3) Firebug & Firepath 1.9 version.
To learn Selenium you can visit the below-mentioned link:-