In simple language brother .. In Computer world we have Windows 7 , Windows xp , Linux red hat , Obunto , Unix , Mac OS , Windows vista . These all are operating systems ( OS ) but provide different softwares and stuff to do our work easily with GUI ( Graphic User Interface )
In Mobile world There is Symbian , Linux , IOS , Andriod , Windows 7 , Meomo , Blackberry OS they are all Operating systems they provide there own made applications to make us do our task on the phone .
Symbian is having versions like symbian 3 , Symbian 9.5 , 9.4 , Symbian 60 , Symbian 90 etc
Andriod is also having version or you can say updates Cupacake,Donut , Eclair ,Froyo , Gingerbread etc
IOS also have got versions in numbers like 3.0, 3.1 , 3.2, 3.3