Seeing as you have jumped from XP to Windows 10, then I'm not surprised you're finding it very different. However, Windows 10 is FINE so please just chill a bit and allow yourself time to find your way around. You might even gain some insight watching some Windows 10 tutorials on YouTube ... There are also some very good books available which you could work through to learn about Windows 10. This OS is more comprehensive than previous systems so there is a lot to learn.
Regarding your question about thumbnails in File Explorer (previously known as Windows Explorer), just take a look at the bottom right of the File Explorer window and you will see two small icons. One is for listing the contents; the other is for a small thumbnail. Just click one or other to change the view. Further choice of viewing in thumbnails or larger can be seen if you click on VIEW to see the 'Ribbon' and in the section labelled 'Layout' you can take your choice.
You are also able to have the 'Ribbon' displayed all the time, or only when clicking 'Home/Share/View' by clicking on a tiny/feint '^', or inverted, on the extreme right from Home/Share/View, next to the blue 'Help' icon
I hope that helps to get you started. Please post back to let us know if you have solved your query and perhaps also tick as 'resolved'