Just plug your phone into your computer using the USB cable that comes with your charger. Skype and Slack have support for things like PDF files, archived (zipped) files, and other document types as well. This should work for smaller files like photos, documents, or similar things. You send yourself the file in a chat on one device and retrieve it on another. Most emails have a limit of around 25MB for attachments. You use the cable to transfer documents to your flash drive or external hard drive or vice versa.
USB On-The-Go – USB OTG cables allow you to connect your device to USB devices such as external hard drives or flash drives.The transfer rates are very slow so only use this method for smaller files. Use Bluetooth – If your laptop has a Bluetooth module or if you have a Bluetooth dongle for your desktop or laptop, you can pair your device with your computer using Bluetooth and send files that way.
If apps aren’t your deal, there are still some other ways to transfer files from your PC to Android and vice versa.