Since custom code is only for paying members I though I'd show all my fellow freeloaders how to create a simple pop-up without any code
Setting up the pop-up
First off, you want to create a section into your page, give it the class modal-background and a transparent black background. Then give it a fixed position and select the Full page option.
Now, place a div within the modal-background, and give it the class modal-window.
Style it as you'd like but you have to have a link block with the class modal-close, and then select the modal-background and select display, none.
Creating the button
Create another link block in your body and call it modal-button and style it as you'd like
Creating the interaction
Select the modal-button and open the objects tab. Go down to interactions and create a new interaction, add trigger and click. Click affect different element(s) and choose modal-background. Add a step on first click and choose display block.
Now select modal-close and repeat the process except this time choose display, none.