I believe those are extra F keys that do nothing, if you are using a PC keyboard that is.
Otherwise they may have been added to your keyboard so that future OS's could take advantage of them. That way people wouldn't have to buy new keyboards. Most people don't have anything higher than F12 though.
Standard keyboards go from F1-F12.
That is unless your PrtScn/SysRq, ScrLk, and Pause/Break keys were replaced with F13, F14, and F15 on your keyboard.
I don't think I've actually ever seen F13-15 on a PC keyboard.
Do you have an Apple keyboard? Those go up to F16. I'm guessing you would have included F16 in your question if you had that..
Insert is a fairly useless key for modern day computers.
Basically, insert is ON by default, meaning that if you bring the cursor back into the middle of a line of text, anything you type will be "inserted" into the line of text without overwriting the following text.
If you push the insert key then you will essentially switch your keyboard to "overwrite/overscript mode", which will REPLACE letters as you type.
Go into a text editor if you want to try it out. A lot of newer programs will just use insert mode by default and not even recognized whether or not the insert key has been pressed or not. I know older versions of Microsoft Word recognized it. Not sure about the newest.
Google Chrome also does not recognize it while I believe Firefox and IE still do.
To this day I cannot think of a use or need for the Insert key.