Units of measurement indicate what is being measured.
The number which precedes the unit of measurement indicates how much it measures.
The following table shows the names and symbols of the units corresponding to the fundamental magnitudes. To see the rest of the physical magnitudes, click here.
Observe how in no case is the symbol followed by a full stop, a very common error. 
Fundamental magnitudes
Units
Name Symbol
Length metre

m

Mass kilogram

kg

Time second

s

Intensity of electric current ampere

A

Thermodynamic temperature kelvin

K

Quantity of substance mol

mol

Luminous intensity candle

cd