Binding to Current/Auth User

I have a table that currently is adding event records. I wanted to logged in user to add events and those events will hold a field for their userID. All straightforward and working. However, I’ve run across this a few times and I don’t have an answer. If I want to bind current userID to a field why is there a dropdown to select 0 through however many users are in my database? I seems that my only binding option is to select a predefined user. If I change this dropdown it will insert the user ID of that user and not who is logged in. What is the appropriate way to bind to the current user?