Unless you have a huge number of users doing heads-down data entry, you are
unlikely to run into locking issues if you use the default of optimistic
locking.  If userA opens a record and makes a change and userB opens the
same record - Access shows a circle with a line in it in the record selector
box.  If userB then tries to save the record, he will be allowed to and when
userA goes to save, he will get an error message giving him three choices -
save over B's changes, discard his changes, copy his changes to the
clipboard and decide whether to apply them after seeing the updated version.

Refreshing will update changed data and will show #deleted# in the fields of
deleted records.  Requerying will rerun the query and so deleted records
will disappear and added records will show along with any changes to
existing records.  If the users stay on the same form all day, you may want
to give them a requery button that they use periodically throughout the day
so they can see any new records.  If they are in and out of the database or
move from form to form, you probably won't need the requery option.  BTW -
Access does automatically refresh forms at the interval specified when you
designed the form but it does not automatically requery.