Even if your backyard is like Mack Male's in Edmonton, Alberta, Canada, seen at the right -- even if you have no backyard -- your home base is a good place to begin thinking geologically.
Geology deals with the Earth's physical structure and what it's made of, its history, and the processes that act on it.
Therefore, to think geologically is to think in terms of processes which have caused the stuff the Earth is made of to be structured as it is. A rock means more to you if you know how it was formed, why it consists of its particular assemblage of minerals, and if you know when the fossil in the rock was a living creature, and what the Earth was like when the creature lived.
On our Geological Processes page we list the processes that act on the Earth, and your backyard, from ordinary erosion to continental drift and meteorites from outer space.
Even if your backyard is just a flat lawn like Mack Male's, there are geological reasons why that lawn can exist on dry land, on a planet mostly covered with ocean. There are reasons why the lawn is flat, and not on a hillside or a mountain slope. And reasons why the lawn is at its elevation, and not much higher or lower.
Thinking about geological processes is a good beginning to thinking geologically, but of course for most of us the fun is in getting to know the details resulting from those processes, as by collecting rocks, minerals and fossils.
By now probably you're getting into the flow of it. Maybe the next step is to browse the links on our Backyard Geology index page.