Use Activity Monitor

Open Activity Monitor from Applications → Utilities or Spotlight. It shows processes using CPU, memory, energy, disk, and network resources.

Start from the symptom. If the Mac is hot and the fans are running, inspect CPU and Energy. If applications pause while switching, inspect Memory. If storage activity is constant, inspect Disk.

Sort the relevant column, then watch it for more than one moment. A short CPU spike while an application exports a video can be normal. A process that stays at the top while idle deserves investigation.

Read memory pressure, not only free memory

macOS uses spare memory for caches. The Memory Pressure graph combines several signals and is more useful than one free-memory number.

Swap use is not automatically a failure. Look for sustained yellow or red pressure, growing swap, slow application behavior, and a process whose memory continues to increase.

Inspect before quitting

Double-click a process to inspect it. Confirm the name, user, open files, and whether it belongs to an application or macOS service.

Try Quit first. It asks the process to stop cleanly. Force Quit ends it without normal cleanup and can lose unsaved work.

Do not force quit an unfamiliar system process just because its name is near the top. It may restart, or other functions may depend on it.

After quitting a problem application, verify whether CPU, memory pressure, or responsiveness improved. Then find the cause: an extension, damaged file, runaway task, or repeatable application bug.

Try this: open one application that performs visible work, observe its CPU and memory during and after the task, and explain why the peak alone is not enough to call it a problem.