Below is an animation showing a simplified lattice, representing atoms as solid spheres and containing vacancies. When you start the animation, the vacancies tend to migrate to the same plane as each other forming a dislocation loop as shown. It is important to realise that this phenomenon actually takes place on a much larger scale involving many more atoms, and that the movement of vacancies is still random, even if biased in certain directions; there's no guarantee the vacancy will reach a dislocation loop.

In addition to vacancies aggregating, interstitial atoms also form discs between lattice planes. This causes distortion of the lattice surrounding it, thereby making it increase in volume. The lines represent planes of atoms, with standard notation representing dislocations.

To better understand what a dislocation loop is, consider this diagram of a single plane. The diagram shows a vacancy loop looking down upon the plane. Note the other vacancies in the lattice.

Now let's consider how vacancy loops travel through the lattice. The following illustration shows the glide cylinder through which the dislocation loop can travel. The b arrow shows the Burgers vector of the dislocation.