@nirsound, If I'm understanding you correctly this time, it sounds like you may be asking how to create link. Well a basic understanding of html is only needed, I know that with WordPress it makes it so easy for anyone to have an awesome website with no html knowledge. Anyway a link is created by defining an "Anchor" such as this:
<a href="http://yoursite.com/some_directory/your_page>Order this Photo</a>
That bit of code would look like this:
Order this Photo
Alternatively you could replace the text with an image:
<a href="http://yoursite.com/some_directory/your_page>
<img src="http://somesite.com/some_directory/some_image.gif">
</a>
As for your second question, that would take the help of the developer of NextGen Gallery to do that and that definitely treads on the breaking point of my abilities, although it could be a nice feature.
good luck,
-Bob