To add pop-upon siteload, you can download the StoreHippo app "Pop-up at site load". This app allows you to create a pop up when the site is loading. The pop up can be of any kind like register pop up, discount pop up, etc depending on the widget, you created.
The following steps allow a user to enable the pop up on the site load:
Click on Visit StoreHippo App Store. It will redirect you to the StoreHippo App Store.
Search for the app Popon siteload and install it.
Click on the Settings of the app.
Click the Edit to provide the widget name and header.
Specify the Widget Name and header for the pop-up in app settings. Widget name: Provide the name of the existing widget here. You can also create a new widget and specify it the app. Header: Enter the tagline you wish to appear in the header of the pop-up.