How do you access Activity Monitor?

Activity Monitor is in your Mac's Utilities folder. Double-click it and it opens. Is yours not doing that?

Utilities is in your Mac's Applications folder.

You can find Activity Monitor several ways: by going to the Finder (select the Finder icon in the Dock) and selecting the Go... menu > Utilities, or by clicking the Spotlight (little magnifying glass) icon in your Mac's menu bar, upper right, and typing Activity Monitor there.

After you open Activity Monitor, drag its icon in the Dock to any other location in the Dock. It will stay there even after you quit Activity Monitor. If you change your mind and don't want it in the Dock any more, drag it away from the Dock until the text "Remove" appears above it, and let go.

How to use Activity Monitor - Apple Support