Transfer data to Android via USB, is the PC the host?

I have some questions about USB.

When I connect my Android device to the computer or notebook and copy a file on the desktop with Windows Explorer to the Android device.

What is it exactly? Read or write? In addition, who is the USB host? Please note that the Android devices use the MTP protocol for a USB transfer.

Again the same question what if I do it the other way round, i.e. In Windows Explorer any file that I see on the Android device and copy on the desktop.

What does external hard drives and USB sticks look like?

As far as I know, the PC is almost always the host.

The mobile phone is the host only in rare cases. For example, if you connect a USB stick or keyboard directly to the cell phone.

https://www.droidwiki.org/wiki/USB_On-The-Go

Ok and what is writing and reading now?

File from PC to Android and file from Android to PC