So, if you'd like to study abroad, perhaps in the USA, it is very likely that you'll be asked to take it because universities want to make sure you'll be able to follow the course and be successful, and for that, you need English.
So, that said, I've been asked quite often what the difference between iBT and pdt is. Simply said: iBT is the internet based test and pdt is the paper delivered test.
Not so simply, the differences are bigger than just format.
The pdt is the new version of the paper test which was used until October 2017. It is available in places where there is no internet and has 3 sections: Reading, Listening and Writing. (Yes, that's true: no Speaking).
The iBT is by far the most frequently used format of the test. I believe 98% of people taking the TOEFL take it online. The tests lasts for about 4 hours (the paper delivered test will take a little less than 3h) and includes all 4 skills: Reading, Listening, Writing and Speaking.