Dayo, sadly, because of the market size, app related business remain only profitable in a few western countries. I don’t know of any that could be used in Nigeria. That said, you can always put your own twist on things and make something that people in your local area could find useful. Essentially, you create a niche market out of it, and that can be very profitable.

_{– Project Payday is one of those sites that has testimonials of people who have earned thousands of dollars by getting paid to get trial offers. I’m not saying you’ll earn thousands, but it is legit and you can earn some extra cash. They assume that by paying you to do a free trial, you’ll either like the product and purchase it, or forget to cancel the trial and get charged for it. If you can keep track and cancel before you get charged (if you don’t want the product), then this is a great site for making some money.}
If you don’t mind doing other people’s chores, then TaskRabbit is a great option for making money online. Earn extra income by walking your neighbor’s dog or mowing Mr. Smith’s lawn. It might seem like not the most lucrative option, but the top taskers reportedly earn as much as $7000 a month, making this a full-time way to make money online for some.
Create a killer course experience: With your course validated and in the works, you need to figure out how people will take it. Most course creators choose to host their courses (after going down the path of learning how to make a website) on their own blogs. This way, they get all the value of bringing customers back to their site on a regular basis. I host my own courses from a subdomain on my own site so I can easily add more. The course experience is incredibly important as well. And after trying most of the solutions, I highly recommend Teachable—an online platform designed specifically for courses.
Now you’ve got many different options to start earning online. If you saw something that really interests you, try it out and learn more about it. If you’re really wanting to make a full-time income online, you need to be dedicated to learning how to do what you want to do. There are tons of free resources out there. You just have to search for them!
While it often takes a significant amount of time and hard work to build up your affiliate income, if you have the ability to regularly publish high quality content that drives in targeted traffic to your website, this online revenue source can become quite substantial. Follow along with my experiment growing two completely new blogs—one finance blog MoneyTalk and one called SmartWP about WordPress, into additional revenue streams for my business.
Mechanical Turk: Amazon's Mechanical Turk is a resource for doing human-intelligence tasks, or as the site commonly refers to them, HITs. You get paid a very small fee for any given HIT and you'll need a good deal of volume to make a substantial amount of money. But it is a resource you can use in your spare time to generate a small income online. 
Be professional. When you submit a résumé, don’t type it in ALL CAPS and please don’t avoid the caps lock like the plague. Know how to use it without looking incompetent. Write in complete sentences with proper grammar. Of course, there will be exceptions, but even with the exceptions, you must keep it professional. You’re building their view of you.
If you’ve got a way with words and expertise in a niche, there are plenty of sites that will pay for articles and content you write. Think of the sites you read regularly. What can you contribute to them that would be interesting? Research your niche and then look for ways to pitch articles. Many sites will simply have a submission or contact link in the footer. To get started, check out my full guide to becoming a freelance writer on the side and then submit your articles to places like Instash, Listverse, A List Apart, International Living, FundsforWriters, and Textbroker.
^{Market your course: The beauty of using a course to make money online is that you can continue to sell it for as long as you’d like. Look for niche communities on Facebook, LinkedIn, or Reddit that might benefit from your content. Guest blogging on relevant sites. Look for anywhere you might be able to get in front of the right people. With just a few hours a month you can continue to generate sales.}
If you’re willing to take on some risk and have the heart of a true hustler, you can make extra money online doing commission-only sales for startups and other businesses. While you won’t be getting a regular salary, with the right sales strategies and skills as an inside sales rep, you can make decent money for each sale you bring in. And because you’ll most likely be working with startups, if you can negotiate a little equity you could profit big time if you're pitching a solid product and the startup succeeds.
Every year, hundreds of millions of documents are notarized in the United States: wills, mortgages, citizenship forms, handgun applications. While for decades, this has all been done in person, there is a budding crop of sites that allow notaries to take their services online. If you’re already a notary, you can sell your services online. Or, if you want to get started, check out the National Notary’s checklist for becoming a certified notary.

Being a blogger is one of the best ways to earn money online. Apart from this one can also make money by playing online real money games. Recently I have found a browser game – Wealth Words. It’s an online crossword gaming website where a user gets real cash money for solving the crossword puzzles right. You can add this to the list as well! It’s really entertaining to play and win.

If you have experience with marketing, SEO, or a knack for getting people excited about the products and services you use on a regular basis, think about refining your skills and putting them to work making money online as a small business marketing consultant in your region—especially if you can become a local SEO expert and can help local clients rank higher in their search results.
You can sell your ebooks through Amazon's Kindle program or Apple's iTunes Connect, which gives you access to a large majority of the digital-book reading market and the barriers for entry are incredibly low. You don't need to invest lots of money to make this happen, but you do need to invest lots of time, not only in writing the ebooks, but in marketing them as well.