When you set up your template and install it, make sure that there is a footer area. You can do this in one of two ways, it is up to you.
You can either abstract out the footer file in your template like they do in the default theme under concrete/default/default.php this line:
You can edit this in your theme which you install in the themes folder, not concrete/themes.
That is one way and a great place to put your google analytics.
Another way is to make an area down there in which you can put a block, i'd say a content block. Install your theme, then you can edit your page type, and add your text down there (or images or whatever). If you want to change this site-wide, you need to change it in the page-type and then click the block in the page type and it brings up a change on children pages or something along those lines. Click that and all the blocks that you edit there will have their changes reflected on every page that was made with that page type.