Hey O, sorry it took me a while to respond,
You don't need a VB editor - Access has one! While Visual Basic for Access is a bit different than normal ol' Visual Basic, it's similar enough to futz around with. You can either create new modules which you can call from different events, or you can code directly into events. So, for instance, you could muck around with the "On Click" event of any of your controls, or have some code run when a report or form opens, and so on. But it actually doesn't sound like your problem has to do with VB too much.
It sounds like your problem is with a popup form, not the subform to the main form, am I right?
(Just in case your problem IS with the subform, here's some help: To find the master-child link, select the properties of the subform (NOT the Form Properties of the subform). It can be difficult to get your mouse to focus on the subform, without focusing
in the subform - try using the dropdown list on the upper left to choose your subform. Then go to properties, and check the Master-Child links!)
If the popup form is going to remain open on top of the forms you already have open, then it is relatively easy to have it jump to the record you want. You can create a command button using a wizard that will open the record you want for you.
If you're looking to make the popup form ready for new orders, then you can change the form property "Data Entry" to yes, and then in the Default Value property of your linked field/Foreign Key you could reference the linked field/Primary Key of the form that is open underneath: =[Forms]![YourMainForm]![LinkedField/PrimaryKey]
Hope that helps! (Sorry again for the delay!)
If it doesn't help, Compact & Repair your DB, put it in a zip file and post it here and we'll see what we can do.