Everything you could want to know is here, if you are good at searching. You can search on a term, but if you know what object the event/method/property applies to, you start with that since this is an object oriented model. I find that brings up less fluff.
In your case, you're working with an Access textbox, so you navigate to Access > Object Model > Textbox > Events and find On Change. There you will see that the event isn't triggered by code. LOTSA info - I go there often.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.