The answer to your Questions is IMGBURN.
Download it … it’s free.
Explanation Windows doesn’t have (decent) inbuilt support for burning CD’s & DVD’s, so you need a proper burning software. There are lots you can try, but imgburn is small, reliable & free.
Version 4.10 is the most current (at time of writing).
Once you install & start it, click “Files to CD/DVD” and you can just drag & drop what you want into them & press burn.
It will tell you the size you’ve used, and what media (CD/DVD/DLDVD) you will need to burn the files you have selected.
That’s all there is to it.