You're not dumb. The only thing you're missing is that acceleration is a change in velocity, not a change in speed.

What does that mean? Picture a car driving down the freeway. The speed is what you see on the dashboard, and the velocity is that plus the direction you're going. Now picture driving around a curve in the freeway. The speed stayed the same, but the velocity changed because you changed direction, and while you were on the curve you felt a sideways force. That force is the result of the acceleration that changed the car's velocity but not its speed.

If that makes sense, now picture a car driving around a circular track. The speed stays the same all the time, but the velocity always changes because the car's direction is always changing. The result is that even though the car isn't speeding up or slowing down, you feel a force - that's acceleration!