The polypores are among the most common, widespread, and easily identifiable groups of wild mushrooms, with some excellent edible species, and only one poisonous species, Hapalopilus nidulans, which to hard and woody to eat, so this is a great group for new mushroomers to study.
Polypores have three features that, in combination, make them distinct:
1. They nearly all grow on wood, such as trees, logs, stumps, or buried wood. That's because these fungi are either decomposers or parasites, or both.
This does not mean all mushrooms that grow on wood are safe to eat. Other types of mushrooms also grow on wood, and some of them are poisonous.
2. Polypores, sometimes also called bracket fungi, are generally shaped like shelves, not like umbrellas (although some are crust-like). If there's a stem, it's usually short and off-center.
Again, not all mushrooms with off-center stems are safe to eat. Mushrooms other than polypores have off-center stems.
3. Polypores all have many tiny holes, or pores, on the undersides of their caps (polypore means many pores). Microscopic spores emerge from these pores. You can usually see the pores (but not the spores) with the naked eye, but sometimes they're so small, you'll need a magnifying glass or loupe to see them.
This does not mean all mushrooms with pores underneath are safe to eat.
Boletes also have pores under their caps, and some of them are poisonous, but boletes grow on the ground near trees, not on wood, they're much more perishable than polypores (some of the woodier species persist for years), and the layer of tubes that leads to the pores peels off from the rest of the cap easily in boletes, but not in polypores.