Can i use an open source library in github to make some animations in my app ?
Yes. Many on envato already use open source code in their projects.
Like many things in life, it depends.
Can Open Source software be used for commercial purposes?
Absolutely. All Open Source software can be used for commercial purpose; the Open Source Definition guarantees this. You can even sell Open Source software.
However, note that commercial is not the same as proprietary. If you receive software under an Open Source license, you can always use that software for commercial purposes, but that doesn’t always mean you can place further restrictions on people who receive the software from you. In particular, copyleft-style Open Source licenses require that, in at least some cases, when you distribute the software, you must do so under the same license you received it under.