The basic Figure of Eight Knot as shown in Figure 1 is a stopper knot in the end of a piece of line which is somewhat more bulky than an Overhand Knot pulled up taut for the same purpose. How to tie it is self evident from the illustration.
Figure 2 shows it tied in a doubled-over line and this is even bulkier. Technically this is termed 'tying a Figure Eight in the bight'.
Two lines may even be joined by this knot. I found it easier to make a loose Figure Eight in the end of one line and then feed the other piece of rope backwards through the knot thus 'doubling' it (Fig. 4).
Tying it around the standing part of the line creates a loop knot (Fig. 3).
Tied in a slightly different way around the standing part of the line, and not actually a true Figure of Eight at all, generates a Crabber's Eye Knot (Figure 5) which may firstly be adjusted for size and thereafter locked by drawing it up taut.