Hey Siddharth,
there are a lot of platforms like fiverr.com or freelancer.com that mediate between freelancers and clients. In order to "earn a bit of extra money" just sign up on one of those platforms and do what you're good at.
Unfortunately, the competition on these platforms is extremely high in almost any field and there are a lot of freelancers that work for "dumping prices". A concrete example would be the design branch: on fiverr, I stumbled across freelancers that offered a basic screendesign for under 5$.
Similar trends can be observed for the programming sector on those platforms. Some freelancers code a basic native iOS app for 250$ - obviously, the quality of such an app won't be high-end, but a lot of clients don't need high end stuff and worry about price a lot.
It's also worth to know that you'll probably have a hard time offering niche-products on there. Most of the clients on those sites are individuals or small businesses, that search for full-stack solutions instead of e.g. just a Node.js server. But hey, might as well be that you'll have a lot of customers - I'm just talking about my personal experience.
So my advice would be to just try it out and offer something you're good with. Just know that competition is huge and pay-off probably won't be too big. Worst case would be that you waste your time creating the profile 🤷♂️.