Activity Monitor lives in the Utilities folder on your Mac, and you can also open it quickly with Spotlight search.

Here are the easiest ways to find it:

  1. Via Finder (Applications folder)
 * Click the **Finder** icon in the Dock.
 * In the sidebar, click **Applications**.
 * Open the **Utilities** folder.
 * Double‑click **Activity Monitor**.
  1. Via Spotlight shortcut
 * Press **Command + Space** on your keyboard.
 * Type **Activity Monitor** (or just “activity”).
 * Press **Return/Enter** to open it.
  1. Via Launchpad
 * Click **Launchpad** in the Dock.
 * Scroll or search for **Activity Monitor**.
 * Click it to open.

Once it’s open, you’ll see tabs for CPU, Memory, Energy, Disk, and Network so you can check which apps are using the most resources and close anything that’s bogging your Mac down.

TL;DR:
Finder → Applications → Utilities → Activity Monitor, or just press Command + Space and type “Activity Monitor” to launch it.

Information gathered from public forums or data available on the internet and portrayed here.