Hi,
As far as i know, you can use text, excel and etc,. whatever you want using below Steps.
1) Keep ready you test case details in text or excel or others.
2) You have to crate functions that can implement and return the individual test case details from your source.
3) Refer this article https://support.smartbear.com/testcomplete/docs/testing-with/deprecated/manual/creating-from-scripts.html to create a Manual test case using scripting.
However, If you want to maintain Manual test cases, it's run status, Bug related to that test case and etc,. you may comfortable with Test Management tools as tristaanogre said and noted.
