how do I move my iTunes library from my laptop onto an external hard drive?

Back up and restore your iTunes library on your PC - https://support.apple.com/HT204318

My one-sentence summary if you always use iTunes' default preferences settings: Copy the entire iTunes folder (and in doing so all its sub-folders and files) intact to the other drive, hold down the option/alt key (shift on Windows) while starting iTunes, and when requested to select a library select the iTunes Library.itl file in the copied folder

Drag the entire iTunes folder there, launch iTunes with the Shift key held down, and choose the other library.

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