I get asked so many beginners questions so often, that in defense of my time, I've decided to do a Tatting 101 with the basics and I thought I'd start with the one that is the simplest, but the one that I still get asked: How do I get the thread on the shuttle?
First, there are different types of shuttles. The most basic shuttle is a flat shuttle. Here is a template for one that you can cut out of an old business card.
On a flat shuttle, take the loop and position it around the shuttle going into the hole on one side, around the back and out through the hole on the other side. Then holding the thread end in one hand and the ball end in the other hand pull and the knot will slip making the loop smaller and smaller until it's snug against the shuttle.