Selenium is the most popular automation tool because there are immense benefits of Selenium for Test Automation. Importantly, Selenium is good for testers because it is:
1. Open-Source
2. Language support
3. Supports Operating Systems
4. Support across browsers
5. Support for programming languages and framework
6. Tests across devices
7. Constant updates
8. Loaded Selenium suites
9. Ease of implementation
10. Reusability and Add-ons
I would recommend this Selenium Certification Course by Intellipaat to start a career as Selenium Tester.
Also, watch this video on the career scope of Selenium Testing: