That's a great question, and one I definitely asked myself before my last purchase! The good news is, for a typical outdoor trash can you buy from a hardware or home goods store, the assembly is usually very minimal. Most of the time, you're looking at a 5 to 15-minute job right out of the box.
Typically, the can itself comes as one main piece. The assembly almost always involves attaching the lid and, if it has them, the wheels. For a standard plastic or metal bin, this often means simply snapping the lid onto its hinges or sliding a pin through a couple of pre-aligned holes—no tools required. For wheeled models, you might need a screwdriver (usually provided) to bolt the axle and wheels onto the base. That's generally it!
You might have a few more parts with a fancy model that has a foot pedal or a locking lid, but the instructions are usually straightforward. Honestly, the hardest part is often just getting it out of the packaging! So, you can expect a very quick and simple DIY task, not a major project. You'll be tossing your first bag of trash in no time.