See the attached two images to visually see where the function is increasing and decreasing. (There's one image for each.)
We identify where a function is increasing based on where the y-values increase as the x-values increase. In other words, as you move left-to-right, the function is increasing if the function is moving upwards.
We identify where a function is decreasing based on where the y-values decrease as the x-values increase. In other words, as you move left-to-right, the function is decreasing if the function is moving downwards.
In both cases, while you recognize where it's one or the other based on the y-values, you describe it based on where it's happening, based on the x-values. The y-values tell you what's happening, the x-values tell you where it's happening.
The function is increasing on the intervals (-infinity, -4) and (-2,infinity). This is the red highlighted portions.
The function is decreasing on the interval (-4,–2). This the the blue highlighted portions.