Normally, you don’t necessarily want to disable the application (often called process) that uses the most CPU, but understand what makes use it as much. Some of them are system-critical, and can only be quit by having the computer turned off (which is not very useful
).
Simply put, CPU usage on Macs is calculated as percentages of core use. So, 50% equals of the usage of half of 1 core.
On a 4-core system, you can have a total use of 400% before the CPU can’t keep up.
There are other factors, like drive speed, memory usage (although your screen capture of the memory usage) will influence a computer’s performance.
To help us, you might want to provide us with a screen capture of the CPU tab of the Activity Monitor when the computer feels sluggish.