In order to find your list subscription form, you have to navigate to your customer area, then from the left side menu, expand the lists menu and click on the Lists link. Doing this, will reveal a page looking like:
Choose the list you want to get the subscribe form for by clicking on the list name or on the list unique id, which will reveal a page like:
From here, if you click on the Form box, you will get the html/iframe code for embeding the form in your site, like:
And if you click on the Pages box, you’ll be able, among other pages, to see the subscription page and the link to it:
So it’s up to you if you’ll embed the html form, the iframe code, or you’ll use the direct link to the subscription form.