1) Sell old things online
Whether it's an old book or an old t-shirt, we all have some things in our homes that we don't use anymore so why keep them if you can sell them and make some extra money? Just take a look and examine different things you have in your room, I'm sure you will find at least 5 items you haven't used for months and they are just sitting there. Just post them on websites like Ebay, because it only takes you 2 minutes to do that.
2) Complete surveys
There are probably hundreds of websites available that require people to complete surveys. Its one of the easiest way to earn extra money in your free time because all you have to do is answer a few questions about different products or services and best part, you can do it using your phone.
3) Start a blog/YouTube channel
We all have a hobby. We all have something we like to do in our free time. So why not share your experiences with other people and get paid for that? Blogging and making YouTube videos are a long term method because it will take some time to attract an audience that follows you and the articles/videos you post. It may take a few weeks, maybe even month until you see some money coming but after you start getting the first payment it becomes easier and faster. If you have succes you could even turn it into a full time job and make money by doing what you like.
4) Write articles
If you are good at writing articles then this is the perfect way to earn some extra money in your free time. A lot of persons need articles to post on their websites but they don't have the time to do that so they pay others to do it. You can get from as low as 1$ per article but it could go up to 50$ for complicated and long articles. Usually you will get around 5$ for each article you write, but it depends on the category of the article and mostly on the length of it.
5) Sell your photos for money online
If you camera is quite decent and you have the possibility to take some unique and great pictures then do it. There are people ready to pay for your photos if they are something who look nice. A website for this kind of service is Shutterstock.