When a character is prevented from easily succeeding in an action, this is known as a Challenge Level. The challenge level is expressed as a number. The character needs to have enough successes on his/her Success check to beat the challenge level. If you only tie the challenge level you don’t fail at the action you simply make no progress. If however you have less successes than the challenge level then you fail at the action and you will need to decide what happens to your character.
Some challenge levels are static. These are things that have consistency and/or reliability. Examples include defying gravity, activating a particular spell or hitting your target with a projectile. The Author may decide that there are factors that warrant increasing or decreasing the challenge level
Other Challenge Levels are set by the Author when the player declares the action. Finding a particular item in the market, picking a lock or surviving in the wilderness are examples
The third sort of challenge level is a Conflict.
Some specific challenges are listed below along with information on how high the CL should be set.