We download and use many software in our devices. Some of them are free, some of them are paid, and some of them are open sourced. Most of the time common users lack sufficient knowledge to differentiate among them.
We don’t have any confusion regarding paid software. We know that we have to pay to use it as we do for Photoshop, Illustrator, MS Office etc. .
In contrast, when it comes to free and open source software often we mix these two things considering them the same. We believe those software which are freely available must be open sourced and software which are open sourced must be available for free. This idea is wrong.
Free means you can get the software and use it for free but that doesn’t mean that the source code will also be available to you. You cannot tweak(customize) the program according to your requirements. Open source means that you can get the source code(free or paid), tweak it according to your needs and then publish it or use it.
A good example to simplify the concept is, suppose you are downloading and using WhatsApp which is free but not open sourced that means you cannot tweak it. On the other hand, Android is a very popular open source project. That means not only you can download the Operating System and use it, but you can also download the source code and tweak the modules to bring the desired changes as per your preferences.