HI Eeman, you basically have two options to become TESL/TEFL certified.
You can either take a training course online or register in a traditional in house course.
Online courses are a great option particularly if you have a limited budget to further your studies or if you have other work and/or family commitments that restrict the amount of time you have available to study.
There is an interesting article on this in the ICAL Wiki at
Qualifications for Teachers - ICALwiki
Hope this helps