Hi @SH_94 ,
Completely understandable - macros almost require a different way of thinking than "standard" workflows.
To recap what we're doing, we're telling Alteryx that we have a list of files (that are read through the directory tool) and that we will pass the filename (with the full directory path) into the macro. This is then what happens in the macro:
1. The control parameter "controls" which field to use as the Filepath & name
2. The action tool updates the input tool to change the input for every new file
3. The workflow runs for each instance of each file and outputs the data
So, to now answer your questions:
In step 3, where we are asking the action tool to override the filename each time the macro is run, we have the following things that are happening:
1. We're selecting the action type - Update Value in the drop down at the top. This does what it says - it will update whatever value you specify in the configuration below
2. Where choosing which value to update - in this case, we want to override the complete filename, as we want the macro to load a new file every time it's run
3. We're telling the action tool which part of the value to update. In some cases, for example, you may choose to update only the directory, or only the file name in the path - in this case, we're checking the "Replace a specific string" box and asking the action tool to override the entire file path. Be very aware that Alteryx simply sees your value in this box as text, so whatever you put in there, it will try to replace if it comes across this value. So in our example, the macro is saved with 1 of the csv files, so every time Alteryx is running, it's replacing that original file name with the new one that you're feeding into the macro. This is the clever part
To answer your second question - you do not need to worry about the columns - Alteryx takes care of that. This is because we configured the interface designer to allow the schema to be different - if we did not change the setting in the Interface designer, Alteryx would not allow new columns (a different schema). So as long as you add a macro output, save the macro and then use the macro as part of the overall workflow (use @afv2688' s workflow as your guide) you should be fine.
On a final note - if you're still getting an error: pay attention to the string that is in the Action tool that @afv2688 used - he would've had to configure that for his own folder, and you of course now need to configure it for yours. I copy images below that show all the areas you need to update.