By referencing the unintuitively named Microsoft Scripting Runtime object library you can write VBA code to access files and folders on your hard disk. This blog explains how, and gives a couple of worked examples.
The easiest way to work with text files in VBA is using TextStream objects - this blog explains how they work.
To make it easier for users of your VBA systems to choose files, you can show FileDialogs on screen. This blog explains what these are, and how to customise them.
In order to work efficiently with files and folders you first need to create a FileSystemObject. This blog explains how to do this!