How to update all users when one makes a change

Hello,

        I am sure that there is an easy answer to this, just not sure how it
is done using best practice. The problem I have an invoicing system and when
someone adds a new item to someone's order or makes a payment against an
invoice, how do you push that information to all the users who currently
have that record open? Or is it better to not let others open the record
while it is open by someone else? Just looking for a bit of guidance on
this.

Thanks