I'll try and explain it like I would to a five year old. I don't run Windows 10, and I've only posted from my wife's laptop once, and we both hate Windows 10. It's the same process though.
1. Click on the small picture icon that is a square with square dots at the corners and a picture of a tree inside of it.
2. A new box pops up that says "Insert Image" at the top. Click on the words "From Computer". Then click on "Select Files".
3 Another new box will pop up. This box is called a file browser and it is your computer's file cabinet. This box must be used to locate your picture and tell Tnet what you want to post. Find the folder, "my pictures" for example. When you see the pictures you want to post inside the correct folder click one to hi-light it. (Hold Ctrl while clicking to select multiple pictures When done you can sefely release Ctrl without losing the hi-lighted pictures.) Now click the button with the word "Open" at the bottom. The box will close.
4. The first box in step 2 will now be shown. Inside this box are the names of the files you selected to display in your post. Now click the center button with the words "Upload File(s)".
Done.
Now you can post an image from your windows device. It seems to work the same in older windows versions, Linux, and Andriod, and if I recall correctly, Windows 10 also.
Good luck! Sorry I'm not Jeff, by the way.