What is Apache license?

Answer 1

Check this link.
https://whatis.techtarget.com/definition/Apache-License

Answer 2

the application or anything under it is free for public use as long as, you include the lisence, make an attribution, write the changes you made if you commiting any change.
You cant blame the creator for any damage are done by using it. Also you cant use their name for your own purpose (ex. Powered by Someone Who Write this Lib)