If you google "MS Access" and "Scanners" you'll get about a gazillion hits on the subject. Here's one
How to Read Barcode Data Into MS Access Databases
The main thing to understand is that entering data through a scanner is treated by Access as if the data were entered through the keyboard. In practical terms this means that all of the events associated with a given Control, such as the Control_BeforeUpdate, Control_AfterUpdate and other events, will fire, just as if you had physically typed the information in, and can therefor be used to accomplish tasks.
At the most basic level, you place the cursor in the Textbox, on the Form, do the scan, and the data will be entered into the Control.
I haven't done this in years, but I would expect there to be documentation that comes with the scanner. Using a scanner is a common approach, these days, and I'm sure that there are off-the-shelf answers for much of this, many of which are probably Access-compatible, out of the box. And they may actually be less expensive, in the long run, than trying to do all of this yourself.
As for the future, you'd probably do well to split your app into a Front End/Back End configuration from the git go, even though everything will be run from a single machine, in the beginning. It'll make things easier down the road, when you'll probably need this to be set up for a Multi-User Environment.
Assuming, of course, that there will be a 'down the road!' Sadly, DME companies are getting to be endangered species!
Hope this helps!
The problem with making anything foolproof...is that fools are so darn ingenious!
All posts/responses based on Access 2003/2007