You have heard right about affiliate marketing, digital marketing and Freelancer etc. You need patient to learn, invest your hard work and wait for the result from these sources.
There are many articles or YouTube videos on these subject. However, please find few more detail on this. You can become a member in any reputed affiliate marketing websites to get referral link and share the link with your friends or family or followers to use and convert it as sale for its commission.
You can become a digital marketing expert by learning online or joining in any reputed digital marketing firm to learn and use it effectively to earn money online.
Freelancer has few online platform (UpWork / Freelancer etc.) to become a member and select the suitable project to execute it on-time to earn money out of it.
It takes time to learn and earn online from these sources for sure. One can't become a rich at overnight or in a shorter duration through these platforms.
Other than these, this (ISC - IndiaStudyChannel) website itself is a main source to earn money online. Free membership, no joing fee, no annual fee, no expenses for domain or webhosting etc. from you except few draft and post it in relevant section of the website.
You can go through each members' profile on how they earn from here (ISC) and its associate Google AdSense (after approval). Try to visit Article / Resource / Jobs / Ask Expert / Admission etc. sections of the website to know how member posting and earning from here.
If you are well versed in English language then you can become an online tutor, writer and on to earn money.
In case if you have knowledge on video shooting and editing etc. then you can become a YouTuber for any niche like an education, training, travel, food or technology etc. - once you got enough subscribers and reasonable traffic to your video submitted, you can then apply for Google AdSense and earn money online.
Online share or crypto-currency trading is one more source. As above said by other members, blogging and eCommerce website creating is few more sources to earn money online.
SEO trainer - if you are Search Engine Optimization expert or profession then you can guide many online.
Digital marketing promoter: There are few brands or company looking for their products to promote them online like an adv. with fewer budget. You can try it.
If you are a coder, you have many chances to earn money online. Like Mobile app development, web development and coding guide etc.
Etsy is a well known website for selling home-made tiny craft items. There are few app, like, online dukaan, where you can sell your product online and make money.
Virtual Assistant is one more option where you can do data entry, or, bookkeeping, or, email management and assist company's head.
Webdesigner or web-developer is one more option by promoting your work online, get job done and get paid.
Social media 'Influencer' is another option where few of them doing their best on this for different brands.
Try to avoid 'Political' post for few buck and don't waste the time unless you are interested in Politics.
Few likes Podcast - Like text type for article or video type for YouTube, you can create some professional audio for Podcast and earn out of it.
You may not only earn money online, some of these might give you coupons, prizes, and gift cards or items other than the cash. Make sure the sources are genuine before doing any task to avoid any disappointment later.