how 2 c the memory used by processes
 

in windows in windows task manager > process> we can see how much memory each process is taking.
how to see the same thing for each process running in linux o.s. ?

you have many tools to look at the behavior of your system.

1- The most commonly used is "ps". it has lots of options, and (if not suffcicient ) you can feed its output to "grep" to filter through.
Please refer to the man page of ps and worked out examples for more informations.

2- "top" gives a real time view of your processes (their ID, memory and CPU usage, ...). Again, refer to man pages for all the options.

top -s
m
is only showing a few of the running processes.
how to see th memory status of all the processes?

u have to execute in batch mode

top -n 1 -b (n is the number of iterations)

u can choose to pipe the output to other process, also.