copyright and fair use
Copyright laws can be overwhelming to understand all the things you can and can't do. One rule of thumb to use when using resources is to make sure you're not using over 10% and make sure you're not collecting money. For instance if you've made a DVD of a performance or school event make sure you only have 30 seconds of a song or you can't charge anything for it.
Edmodo is a private community where you can set up class online activities or join other professional development communities. It is similar to what you might see in Moodle, but it can't do as many activities. There are a number of public communities you can belong to such as Discovery Education, ISTE, Glogster EDU, VoiceThread, etc.