How do I read a file path that is stored in a textbox?

I know I'm probably missing the forrest thru the trees here, but I can't seem to figure this out.  I can get the selected file path to populate a text box using the open file dialog box.  But then how do I get my application to read from that selected file location (ie. read from the textbox)?  I remember having to do this in class years ago when I took VB but now I can't find any of those old files of code.
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