Photoshop is a widely used photo editor that can be installed on a Mac for free. To install Photoshop, you will need to first create an account on the Adobe website. Once you have created an account, click on the “Create a new account” button and enter your name and email address. After you have created an account, click on the “Download” button to download the installer file. After you have downloaded the installer file, open it and follow the prompts to install Photoshop. Once Photoshop has been installed, open it up and start editing your photos!