We are currently living through the digital age. Making sure that your products and services are marketed on the internet are quite an important requirement in order to be successful.
I would say that there’s no fixed way to learn digital marketing, but experimenting with different strategies, seeing which campaigns worked better, etc, is one way of becoming a digital marketer.
If you wish to start off with the basic terms, I suggest you read blogs which will teach you the key concepts required.
There are a number of Digital marketing books available today too: Digital Marketing for Dummies by Ryan Deiss and Marketing 4.0: Moving from Traditional to Digital by Philip Kotler — are two books which I would suggest you read to gain a better understanding.
The next step would be to take up a course on Digital Marketing, there are a number of courses available online. Do take up a course, this will help you with the theoretical aspects. If you are clear with the theory then you can start implementing and trying out which strategies will be helpful for you!