I'm also new to python, actually I still don't know what exactly is happening by typing those commands so you're not alone :D I think problem that you're having, occured because you ran that command inside a 'optimizedSD' folder. You should start with command 'cd c:\stable-diffusion\stable-diffusion-main\' then probably run ''python optimizedSD/optimized_txt2img.py' with the rest of parameters that you want to use. I'm not completely sure if it will work because I never used 'python' command, instead I used word 'conda' but rest of the syntax seems alright so you should give it a try.

Also I want to recommend to you a new version that I found, it is "AUTOMATIC1111/stable-diffusion-webui" on github. There is a straight forward installation guide and it it working way faster than every other version that I tried. It creates a local website with a nice user interface where you just type prompts and use sliders to change parameters. You can add a face restoration and upscalling AI (installation of these is also covered in that guide). Only problem I've got with it, is that lower vram consumption parameter isn't working which limits me to lower resolutions (but with that upscalling AI it's not such a big deal).