To add a new icon button layer to your email design, you can click on any Column or Hero layer, then select the Icon Button option from the Quick Add dropdown menu, then click the Add + button to insert the new button layer into your layout.

Alternatively, you can select one of the preset components under the CTA tab in the plugin, clicking the Icon Buttons sub-category tab, then clicking any of the icon button component preset options to add them as new "Row" layers to your design.

After styling the button to your liking, you can specify the clickable URL by clicking on your Button layer in Figma, then clicking the Settings button, and pasting your URL into the Clickable URL Link input field; this will ensure that your button opens up that URL in the browser when it's clicked.