Transferring .mp3 files (audio books) from my PC

Hello, I'm new to the forum and also feels like new to the digital world so thanks for your patience if this is a very silly question. I have iPad Mini from 2~4 years ago. I have several .mp3 files ranging from 50MB to 200MB downloaded to my external hard drive. Those are audio books and I'd like to listen to them during my 2-hour commute. I used to be able to just email them when the files were much smaller, but anything beyond 20MB doesn't work very well. I do not have iTune account and prefer not to use iTune. Are there any more "analog" ways, like using USB cables, to connect 2 devices and transfer files? Also, I'd appreciate the recommended apps if I shouldn't be using the default program. Thanks Much!!!!