After buying and downloading the ZIP file of the module, navigate in your PrestaShop admin panel to Modules > Module Manager, and click on the "Upload a Module" button. Drag & drop or select the ZIP file and wait for the modul to be installed.
After the module will be installed, click on the "Configure" button in the confirmation window.
In the LiveAgent module configuration screen, navigate to the "Settings" section, swap the "Enable" option to "Yes", and insert the integration script of your LiveAgent chat button into the "Code" text area. Lastly, save the configuration. Refresh your page and your LiveAgent chat button will be displayed on your PrestaShop website.