If Flash is not installed, which is by default on all new Macs, here's a step-by-step guide to install it safely.
 
Visit the Adobe Flash Player page.
 
Click the Download now button.
 
The installer will download to your computer. If you're using Safari, the file will go to your Downloads folder. If you're using another browser, it may ask where to save the file.
 
Open your Downloads folder and find the .dmg installer file.
 
Double-click the Install  Flash Player file.
 
 After Effects  Flash Player. Read the message carefully to make sure that it's the file you just downloaded. Click Open to proceed.7. Agree to terms and conditions by clicking a checkbox.
 
8. Click the Install button.9. In the window that appears, type your username and password.
 
10. Click the Install Helper button.
 
11. Click Allow  to install updates (recommended).
 
12. Click Done.
 
That's it. It's also recommended to relaunch your web browser after installing Flash.