How do you determine intervals on which the given function is increasing, decreasing, or constant

There isn't a function in the question, but in general: a function is increasing when the line is going upwards, even slightly. a function is decreasing when the line is going downwards, even slightly. a function is constant when it forms a straight line.

a function stops increasing when you hit the maximum point where it is no longer increasing, but turning back around to decrease. similarly, a function stops increasing if it hits its maximum point, then levels out to become constant. the same thing applies to decreasing. do you have a specific function that you need help with, or was this a general question?