How to inject my custom code in cart page?

I am new to square space. 

I am looking for some ideas and example for injecting custom code into cart page. with all details of cart page(product, price, quantity etc.)

regards, 

Which code do you want to insert? Can you send, we can help easier

I would like to add a Button on checkout page on click that button i can popup or get all the details of the page. like cartToken, product details, price, address etc., 
Is this possible ??

Add button is possible with some code

Add button with lightbox, you will need to use plugin

Lightbox show cartToken,.. >> It is dynamic info or fixed info? If dynamic, I believe it is not possible

Thanks for the information. 

I would like to know, 
Can we empty the cart by code like if user change the  tab or page something like that.