Digital marketing is directly related to internet. So before briefing about digital marketing, let us know what the internet is.
According to statistica, India had nearly 700 million internet users across the country in 2020. This figure will grow to over 974 million users by 2025, indicating a considerable market potential in internet services for the South Asian country. India was ranked as the second-largest online market worldwide in 2019, coming second only to China. The number of internet users was estimated to increase in urban and rural regions, indicating a dynamic growth in access to the internet. There were 624.0 million internet users in India in January 2021. Internet users in India were increased by 47 million (+8.2%) between 2020 and 2021, according to datareportal. 
These are some statistics showing the usage of the internet in India.

Now, about digital marketing, Digital marketing is the act of promoting and selling products and services by leveraging online marketing tactics such as social media marketing, search marketing, and email marketing. In a simple sense, Digital marketing is simply marketing your products digitally.

A market is meaningful where you can find a lot of crowds together—the chances of selling your product increase if you are marketing in a crowd. In digital marketing, it is known as traffic. The more the traffic, the more chances are to sell your product.
Above is one way of thinking about marketing your product. This is what all the beginners in digital marketing do. But, these tactics are not usually helpful.
There are specific rules which every digital marketer needs to follow.

Rule no. 1 is, a digital marketer needs to make the right offer at the right time and in the right place. Today, customers are online:

Digital marketing puts you in those same channels, so your best prospects can see you, learn more about your product and even ask questions to learn more about your products and services.
Talking about the right place, one needs to know how the platforms work. The first is social media.
In India in 2021 January, Four hundred forty-eight (448) million social media users were active. A remarkable increase in active users was registered between 2021 and 2020 January by 78 million users (according to datareportal). Devices used for social media platforms are mobiles and desktops, from which mobile leads in usage. Social media contains a vast audience knowledge. The digital marketing experts know how to use the ability to build the correct audience according to the product features and usage. Setting an audience shows you the difference between an expert and a beginner in digital marketing.

Search engines: A search engine is a platform where users go to search their queries. A query could be search-based, knowledge-based, usage-based, or product-based. The search results can influence a user. Google, Bing, Baidu, Yahoo! Are some of the search engines available online. From which, google leads the searches with 70% of the market share. Additionally, google captures almost 85% of mobile traffic.
The enormous traffic potential makes Google a viable option when aiming to capture organic or paid search -- the downside, of course, is that almost everyone is competing for the same traffic.
Plus, recent changes to Google's algorithm, like featured snippets, aim to fulfill user's needs directly on Google, so they don't need to click any links. These changes, and Google's popularity, might make it hard for you to capture the website traffic you want.

Bing, Google's biggest contender, rakes in 33% of U.S. searches and also powers Yahoo, the U.S.'s third-biggest search engine. Bing's search pages look remarkably similar to Google's, with the same categories and a similar white background, with blue links and green URLs. (source of information: hubspot.)

  Online presence is necessary to cover the customers who are aware of the product, want to take knowledge about the product, or even customers who don't know about the product but are finding a solution for the specific problem. In all the cases above, Digital marketing provides you a market with a particular type of customers. To make a robust digital presence, digital marketing gurus guide you by various on-page and off-page SEO activities.

Having a strong digital presence will help you in multiple ways:

Learning Customer' behavior and analysis through efficient tools is essential for optimum results. For online presence, Google Analytics provides you all the necessary analyses. Using these analyses, users can bring more focus to the strategies for the upliftment of the customers.
Right from selecting the website's keywords to bringing it to the top, Google analytics helps a lot by giving all the online structure data.