How to determine directory sizes

[Sampson, Warren]

My 'var' folder/slice/partition (I never know the correct term) is
currently using over 3G and I want to know where and/or what is using
it. Now if I was in Windows I would just "right-click" on the
subdirectories and get the properties which would tell me how much that
directory has underneath. I would then repeat the process as needed.

I've already looked in all the usual places that I know to look
(/var/log, /var/amavisd/quarantine, etc.) but I have not found anything
major.

How can I do something similar from the command line in OBSD and is
there a better way that I am not aware of?

# df -h
Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/wd0a      502M   78.2M    398M    16%    /
/dev/wd0d     1006M   52.0K    956M     0%    /tmp
/dev/wd0e      3.9G    1.5G    2.2G    41%    /usr
/dev/wd0m      7.9G    3.3G    4.2G    44%    /var
/dev/wd0h      2.0G    116M    1.8G     6%    /home
/dev/wd0p      9.8G    2.7G    6.7G    28%    /backup

Thanks,

Warren (Sam) Sampson