Now, there are two basic types of wood, hard wood and soft wood. Lots of people (used to include me too) naturally think that a hard wood is, well, hard and soft woods are not hard. This is kinda true, and kinda not. It depends on context.
In what could be called tree scientist terms, a hard wood tree is one from a broad leafed tree, like an oak. The scientific name for these kinds of tree is angiosperm trees. A soft wood tree is of the conifer trees, or what you might commonly call a Pine Tree.
However, broad leaf trees can have a soft texture to the wood, not being very dense (for example, poplar), just as some pine types can have a very strong dense wood (like Cedar, durable enough to be siding). We'll discuss wood types in more detail below, making sure to stick to what you'll find most commonly in Michigan. If you want to go out of state to get wood, you can, but kinda eliminates the point of saving money on heat by burning wood over gas...
I also want to talk about the differences between seasoned and green wood (and why you avoid burning green wood), and the responsible harvesting of burning wood, both for maximum heat and so it's there for later generations. We'll get to those later.