There ARE several ways to secure a bun . . .
I think one of the easiest ways is to tie your hair up in a pony tie (no metal, of course). Twist your hair until it twists up on itself, and wrap it around the pony tail base. Then get a scrunchi and wrap the scrunchi around the bun. This is called a scrunchi bun

.
Eventually you can do a bun without having to secure the pony tail first. You might want to get some "hair pins". They are plastic and u-shaped. They hold your hair nicely. You can use snoods, hair sticks, hair forks, various clips/clamps/etc, or cages. When you hair gets longer, you might be able to put your hair into a bun without ANY way to secure it, except wrapping your hair up!

LOL That has been my lifesaver! I can't stand going all day with my hair down, so I have to have a way to put it up!
HTH
???/ 35/ 36
2aF/Mii
"Heaven-spun gold" with a sprinkle of gray
~~*~~
Never think that God's delays are God's denials.
Hold on; hold fast; hold out. Patience is genius.
-- Comte de Buffon