‘Plane’ is really a misnomer. The surface of the infinite plane curves, just like the surface of our own familiar Earth. Unlike the curving surface of the Earth, however, the Infinite Plane never crosses itself. It is an open surface, that one can travel across for as many lifetimes as one wishes and neither reach the end, nor come back to the beginning.
Many races think they are the masters of the plane, with only a few rare specimens having ever traveled so far as to encounter a land dominated by those of other races. Humans are one such race, and there are many others. Travel far enough, though, and the intelligent life will be dominated by beings so alien to one’s own self physically, socially and mentally, that they can only be honestly described as ‘things’ from one’s own perspective. Of course, from their perspective, you qualify as a ‘thing’ as well. If they even have such a concept as thing.
It’s not so bad as it sounds. Within the infinitesimal area you are ever likely to cross, there are things that are strange and wondrous, but not so alien as to be beyond comprehension. Those who choose to abandon their own current paradigm and wander the plane can be rewarded by strange treasure almost beyond their imagining, friends and delights that are unknown to the hidebound and the sessile.
Take care, though. Distance across the plane changes not just the specifics entities, but the very laws of nature. And of course, no one ever said the plane was homogeneous, even over small areas. The alien and the fantastic probably exist right by your doorstep, if you ever cared to look. The Plane is truly infinite; everything that exists can happen, has happened, will happen. Whether it happens to you, and how it changes you, and you change it, is of course your own decision.