multitasking on the unix pc

[Tom Baas]

On the unix pc, using the windows you can 'resume' various kinds and various
numbers of operations.  Ok Neat.  My question is how can one do this
without using the windows? I know for example that: ls -l>file& will
perform a list into file 'file' in a background mode.  But, how can 
you get several tasks running to wait till you come back to them - such
as with the 'resume' or 'suspend' button on the att unix pc?

Or.. another question on the same subject... How do the windows actually
allow this.

I would be interested in knowing the answer to the above and appreciate
anyones help on this matter.

Thanks in advance.    :-)

                                Tom