Hi Alfred. I'm Greg, a volunteer installation specialist and 8 year WIndows MVP here to help you.
Easiest is to sort your files into the User folders for your account: Documents, Pictures, Music, Downloads, Desktop, etc.
Then drag or copy those folders to the External for transfer and safe keeping.
Safely remove and change the external to the new PC, Open each folder, on Home tab Select All, then drag or right click to Copy the group to the corresponding User folder on the Explorer bar to the left. If in doubt find the destination folder under This PC, then C:\Users choose your Account.
Confirm the files all transferred by right clicking both the source and destination folders to view their Properties to make sure the sizes match exactly.
Now a word about backup going forward. Your files should always be backed up if you value them at all because the hard drive can die at any time.
Some suggestions to help ease into this habit:
You can drag 5gb for free into OneDrive app to store in the cloud where they are safe from fire and theft.
If you install Google Drive, you can use their new Backup to choose User folders (Documents, Pictures, etc.) to sync up to 15g for free to their cloud.
Or you can drag or copy them to a USB external or flash drive.
Here's how to drag, copy or move large groups of files: https://www.pcworld.com/article/2086566/the-man...
I hope this helps. Feel free to ask back any questions and let us know how it goes. I will keep working with you until it's resolved.