What can I monetize?
Video game content may be monetized depending on the commercial use rights granted to you by licenses of video game publishers. Some video game publishers allow you to use all video game content for commercial use and state that in their license agreements. Likewise, videos showing software user interface may be monetized only if you have a contract with the publisher or you have paid a licensing fee.
What can't I monetize?
Without the appropriate license from the publisher, use of video game or software user interface must be minimal. Video game content may be monetized if the associated step-by-step commentary is strictly tied to the live action being shown and provides instructional or educational value.
Videos simply showing a user playing a video game or the use of software for extended periods of time may not be accepted for monetization.
You can find more information on copyright law and fair use here:
World Intellectual Property Organization