It's very simple. There are basically three kinds of clouds: Cirrus, Cumulus and Stratus. Those can be subdivided in a bunch of types that derive from these. When you see the word Nimbus (or nimbo) either at the beginning or the end of a name, it indicates that there is rain, hail or snow falling from that cloud. In fact; clouds itself are made up entirely of water droplets or ice particles. Some clouds indicate fine weather, others tell that there's a storm approaching. Those are my favourites. That's it. Simple right? Now I will elaborate a bit on the different types of clouds:

 
NAME
HEIGHT
DESCRIPTION
REMARKS
stratus 0-1500ft Whitish, grey layer, often covering hills. May give drizzle.
cumulonimbus 1500-6500ft Huge towers of heavy dense clouds. The tops are flat, usually spreading. Often bring showers and thunder.
cumulus 1500-6500ft Detached dense clouds with sharp outlines and rising domes, mounds or towers. Associated with sunny weather and scattered showers.
stratocumulus 1500-6500ft Grey or white rolling patches or sheets. Bring dull weather, sometimes with drizzle.
nimbostratus 3000-10000ft Dark grey cloud layer, usually diffused by rain or snow. Ragged patches of stratus may occur below the layer.
altostratus 3000-10000ft Flat, thick blue-grey sheet. Indicates rain or snow if associated with cirrostratus.
altocumulus 6500-23000ft White or grey rounded clouds, Usually break up leaving good weather.
cirrostratus 16500-45000ft A transparent milky veil which can be fibrous or smooth. Indicates rain later.
cirrocumulus 16500-45000ft Thin rippled sheets of rounded clouds. Form on the edge of unsettled weather.
cirrus 16500-45000ft Fibrous or hairlike clouds with a silky sheen.  An indication of bad weather to follow with strong winds at the cloud level.
nacreous   Mother of pearl clouds found very high over mountains, usually lit by sunlight.  
noctilucent   Very high bluish clouds, probably cosmic dust. Normally only seen in high latitudes.  

 

Study the picture below and try to find my favourite clouds:

 

Schematic diagram of a thunderstorm:

 

Finally; these are the weather-map symbols for clouds in the USA: