Quotacheck is used to scan a file system for disk usages, and updates the quota record file "aquota.user" to the most recent state. I recommend running quotacheck at system bootup, and via cronjob periodically (say, every week?).
Repquota produces a summarized quota information for a file system. Here is a sample output repquota gives:
# repquota -a
Block limits File limits
User used soft hard grace used soft hard grace
root -- 175419 0 0 14679 0 0
bin -- 18000 0 0 735 0 0
uucp -- 729 0 0 23 0 0
man -- 57 0 0 10 0 0
user1 -- 13046 15360 19200 806 1500 2250
user2 -- 2838 5120 6400 377 1000 1500
Quotaon is used to turn on quota accounting; quotaoff to turn it off. Actually both files are similar. They are executed at system startup and shutdown.