...you practically write the "input_text_file.inp" using any text editor program (e.g., Notepad). The structure and keyword syntax of the input file content must follow the ABAQUS documentation (ABAQUS User's Manual and ABAQUS Keywords Reference Manual are probably the most helpful).
Then you submit 'input_text_file.inp' to the ABAQUS Solver.
I see this being somehow similar to having the FORTRAN text source file (which can be written using any text editor) submitted to the FORTRAN compiler.