Questions about fields and error checking

[Admin]

Last one for the night. 

If someone enters nothing in a field, how
do I error trap that? 

How do I make fields mandatory? - such that the
form will not continue until all mandatory fields hold data 

If someone
presses the submit or save button, how do I check to make sure all
fields are filled in properly? 

Sorry guys. I know how to use database
creation programs, but LiveCode is very manual. Nothing automatic about
it. 

Last one. How do I hide text (or replace it with a bullet point)
for a password field, but save the text in a special variable that I can
write to the database? Same goes with reading the password back. 

I
appreciate all the help I can get. 

Mike