Is a Nikon cool pix L840 a DSLR?

Just trying to figure this whole camera thing out.

No. It's a "bridge camera". It's basically a feature-rich version of the same technology used in digital compact models but with a larger optical zoom lens than normal and styled to look like a dSLR. That means digital Single Lens Reflex.

All SLR and dSLR models have optical viewfinders and because the same Single Lens is used to take the photograph and to reflect a live image to the optical viewfinder the camera is called a Single Lens Reflex. Bridge cameras do usually have a separate viewfinder but it just houses a smaller version of the rear LCD viewing screen so it's not an optical viewfinder.

Bridge cameras don't have the large low noise image sensors of dSLR models and their lenses aren't interchangeable, but some SLR models have had fixed lenses as well. The only distinguishing feature of an SLR model is how the optical viewfinder works.

Nope. Nikon cameras that are DSLR's have a D as the first letter in their model number.