It's short and sweet!

du -hs *

If you run this command it will tell you the sizes of all the files and folder in the current directory.

The -h flag is for human readable format and the -s will give you the size for each file or directory.

If you're looking for the system disk info

df -h

And the output will look like this

Filesystem      Size   Used  Avail Capacity iused      ifree %iused  Mounted on
/dev/disk1     233Gi   43Gi  189Gi    19% 1243927 4293723352    0%   /
devfs          182Ki  182Ki    0Bi   100%     629          0  100%   /dev
map -hosts       0Bi    0Bi    0Bi   100%       0          0  100%   /net
map auto_home    0Bi    0Bi    0Bi   100%       0          0  100%   /home