Copyright is a law that protects creative works from being used without permission. There is an exception called "fair use" that allows limited use of copyrighted material. Works in the public domain are not copyrighted and can be used freely. To use images, text, music or videos from the internet, you need to check if it is public domain or abide by time/word limits for fair use. Just because a work does not display a copyright symbol does not mean it is not copyrighted. You should always properly attribute sources and seek permission from creators if copyright is unclear.