The free command displays the total amount of physical memory and swap space for the system as well as the amount of memory that is used, free, shared, in kernel buffers, and cached.

             total       used       free     shared    buffers     cached
 Mem:        645712     549720      95992          0     176248     224452
 -/+ buffers/cache:     149020     496692
 Swap:      1310712          0    1310712
 

The command free -m shows the same information in megabytes, which are easier to read.

             total       used       free     shared    buffers     cached 
Mem:           630        536         93          0        172        219 
-/+ buffers/cache:        145        485 
Swap:         1279          0       1279

If you prefer a graphical interface for free, you can use the GNOME System Monitor. To start it from the desktop, go to System => Administration => System Monitor or type gnome-system-monitor at a shell prompt (such as an XTerm). Click on the Resources tab.