How can I transfer my iTunes Music and a host of other files from my Win 10 PC

I have attempted to get support from Apple (three occasions) and all I get is links to help items none of which I can understand (my first apple laptop MacBook Air) They appear not to be intrested in the issues I am having and simply cut me off mid conversation.

I am not a techno guru and my 84 year old mark one computer is a little 'off beam' with my new laptop modus operandi however I am still compus mentus and able to deal with most day to day technology issues, however I seem to have come up against a wall of incompetence.

I would like to have a step by step approach to deal with the issues at hand, which are: Transfer of iTunes libaray to my MacBook Air ( The account for my existing iTunes is different to my account for the MacBook - don't lets go there!)

Transfer around 250GB of working files from PC to a 1 TB Weston Digital 'My Passport' portable hard drive. I want to use this device with my MacBook for file storage and to access files etc from the portable drive so that I can open and use them, eg word processing, material already saved for my book writing projects etc. (all the apps will be stored on the MacBook drive - when I find out how to do this!)

Sorry about the diatribe but I hope it is reasonable clear to whoever can help me achieve my goals.

[Re-Titled by Moderator]