some basic confusions . . . ?

[asad.buntu]

hi 2 all !
i have got 2 things 2 ask here !!!!

how can i check the packages whether they r installed or not....
mean via what commands.....?

&

where does these package are installed then , mean which directory......?

[utnubuuser]

read up on apt

[lisati]

Have a look at these menu items:
System->Administration->Synaptic Package manager
Applications->Ubuntu Software Center