Creating SUBSCRIBE NOW Button pls!

Hey All. I am trying to create a SUBSCRIBE NOW button, and place that button next to my homepages main navigation ideally. I have created the subscription product and qualify w the advanced commerce plan. I can't seem to now create the button to then connect to my either a) pop up promotional window or b) subscription product in my store. 

Help please. my mind is melting. 

Nikki 

Here is a guide for adding a button, directions are a bit different for 7.0 than for 7.1 so choose the right one for your site. 

https://support.squarespace.com/hc/en-us/articles/360000293128-Adding-buttons-to-your-site