Firstly you have 100% control over how you want to share your library:
- You can share a library with another user
In my libraries section, navigate to "more operations" button which is next to share and delete icons:
Then click on "Folder Permission"
You can choose if this library is read-write or just read-only
2. You can share with any group that you belong to. You can also choose to give read-write or just read-only permission.
Now the next logical question you may have is how do you manage group permissions, read here: How to manage group permissions