You can't always take screenshots of a game or produce videos featuring the game. The licence requirements for the product from which you intend to use material needs to be checked first. You can find these licence requirements for most computer programs on the company websites.
One example of this is Blizzard's Video Policy, which supports community-created images and videos of their products as long as you don't use them for commercial purposes. However, publishing such content in a Hub is considered commercial use, so I suggest you read every policy closely.
When you are allowed to use screenshots and videos, always include a specific acknowledgement of the product in the attribution including the company name and the name of the product. Also, screenshots should always appear as they would in the software product.
That's true as long as the screenshot or video does not illustrate how to take certain steps in order to accomplish some task. For example, talking about games, making a video or taking screenshots to illustrate how to beat an enemy does not fall under fair use.
Think you know movies? Play along. Challenge yourself and your peers to their movie knowledge. All you have to do is be the first to answer what movie goes along with the latest screenshot. If you are correct, you get...