1. Double-click the zip file to extract the app (if not extracted automatically).
2. Drag the app to the Applications folder (Optional).
3. Double-click to open the app, then close the warning dialog.
4. Open the Apple menu > System Settings > Privacy & Security.
5. Go to the Security section (You may need to scroll down).
6. Click the Open Anyway button (Available for one hour after you try to open the app).
7. Enter your login password, then click OK.

For older versions of macOS :

1. Double-click the downloaded zip file to extract the app.
2. Drag the app to the Applications folder (Optional).
3. Control-click or right-click the icon of the app.
4. Select Open from the top of the contextual menu that appears.
5. Click Open in the dialog box.
6. If prompted, enter an administrator name and password.