Cumulus: tops are rounded, puffy, bright white. Bottoms are flat and dark
Stratus: hang low in sky, flat, resembles fog
Stratocumulus: low, puffy, have patches where you can see the sky
Altocumulus: white or grey patches, form in parallel bands
Nimbostratus: cover sky in a dark grey layer, thick enough to cover sun
Hope this helps! I got some of this information from thoughtco.com