I'm building an app that contains an open source package protected under EDL license
Can I sell it? Do I need to specify something in my app's license? Do I need to give it away as open source also?
You can sell it. It is a permissive license.
If you sell it and use a binary format to distribute, you better read this:
"Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution."
This means, you should add a NOTICE file and a LICENSE file (or something similar) to your distribution. THe Notice file says something like: "includes software by xxx licensed with yyy see LICENSE". And the LICENSE file should contain the actual license.
Please ask a lawyer for details. OS regulations are not easy and differs from country to country. But the direction should be fine.