The program used to display memory information is free. It displays usage information of both RAM and swap. Running it at the terminal will produce the following output;

$ free
             total       used       free     shared    buffers     cached
Mem:       2571088    1605784     965304          0      48316     589324
-/+ buffers/cache:     968144    1602944
Swap:      4393768          0    4393768

By default the program outputs display in kilobyte’s unit. To have it in Megabyte, simply add -m to the parameter when running the program;

$ free -m
             total       used       free     shared    buffers     cached
Mem:          2510       1568        942          0         47        575
-/+ buffers/cache:        945       1565
Swap:         4290          0       4290