Checks or Tests are events where your character's stats, equipment, and possibly a random element decide if you pass or fail. These events range from mundane things such as looking through a phone book for a number to seeing if you can alter the runes on the magical array to disrupt the cosmic horror coming into your world. It is preferred and even suggested in some rule books for checks to only be used when something is difficult, contested/hindered by something, or vital for something to happen (read: the GM's girlfriend wants to do something).