For example... I have txt file called New and txt file called Old... How can i create batch script to check both txt files and then create new text file with lines that aren't in both of them (New and Old txt files)? Thanks in advance...
I assume you meant to ask
How to check lines in two txt files and save lines that aren't in both of them in new text file?
A good command line tool is diff which you can get here for Windows. If that's what you are looking for then How can I get diff to show only added and deleted lines answers your question.
This question https://superuser.com/questions/56603/what-is-a-good-text-comparison-tool-for-windows lists comparison tools for Windows.
Wikipedia has a list of text comparison tools.
FC new.txt old.txt > diff.txt
You can also check the ERRORLEVEL of FC to have your script respond to the files being different.