How make the footer stick to the bottom?

Hello,

I was wondering if there was an easy way to make the footer sticky. The footer is fine on longer pages, but for pages with less content the footer is in the middle of the screen. How can I fix this and add a background image?

@erikasbor

You don’t even have a footer on website that you posted earlier. Are you working on a different website or I am missing something? If you are working on a different website please post your website URL and I will try to help you from there.

Im working on the same website e-buhalterija.lt
To add footer image i using this:

#site-generator {
background: url(http://www.e-buhalterija.lt/wp-content/uploads/2015/06/111.png) repeat-x 50% 20%;
border: none;
min-height: 171px;
height: auto !important;
height: 171px;
overflow: hidden;
}

But footer not sticking to the bottom of page…