Lets say formA is the name of the form that has the info you want and formB is the name of the form that has the field where you want it to go.
Place code like this into an event on formA once that data has been entered:
Forms!formB!controltogetinfo=Me.fieldwithinfo
Or place this code into an event on formB to pull the information from formA:
Me.fieldneedinginfo=Forms!formA!controlwithinfo
Of course, replace formA, formB, controltogetinfo, fieldwithinfo,fieldneedinginfo, and controlwithinfo with the actual names of your own controls.
As to which event to place these code snippets into, that's up to you. You can attach them to the click event of a command button or the AfterUpdate event of a text or combo box. Up to you.