if you have man pages in your system you look at this ;
vmstat 1 20 :gives virtual memory stats. 20 times 1 is the period (1 second)
or vmstsat 1 or else
ps -ef :gives systemwide results
rocesses stats
ps aux :gives some other systemwide results
rocesses stats
sar 1 1 or sar -P ALL etc sar gives cpu stats ( vmstat gives this information additionally to memory stats. But sar gives detailed info for all cpu )
netstat -v |netstat -D |netstat -i|netstat -r |netstat -in or etc.gives networtk stats
iostat 1 10 gives io stats
filemon gives filesystem stats
topas uses this underneath : sou you must read these from man pages