Digital Marketing is booming industry and most of all the businesses are using digital marketing as their one of the marketing strategies to promote their product and services to their desired consumers. There are many online learning platforms are offering the both the paid and free courses to learn digital marketing fundamentals, but we would suggest that you can complete this 100% course offered by Google and accredited by Interactive Advertising Bureau (IAB). Also, you will get a certificate from The Open University post completion of this course. This course is packed full of practical exercises and real-world examples to help everyone to turn knowledge into action.
If you are a book lover, I would suggest this book to learn Fundamentals of Digital Marketing written by Puneet Singh Bhatia and published by Pearson to understand better.