newbie & programmin custom forms

[Dale]

I have a custom form that resembles order entry. When
the property of the order# (field name ORDER) changes the
request is to retrieve order information i.e. po#, ship
to info & item info from 2 sql databases and return this
info to the custom form. This will eliminate re-keying
of data and keying errors.
Being new to this, how does on go about performing this
type of request?

Thanking the experts in advance.