A flip-up backup iron sight set is a pair of small mechanical sights - one front, one rear - that clamp to a Picatinny rail and stay folded flat until needed. On a rifle that normally runs an optic, they lie low and out of the way so the optic's view stays clear.
Their whole job is to be a fallback. If an optic loses power, gets fogged or cracked, or is knocked loose, you push each sight up until it locks and aim with the front post and rear aperture. There are no batteries or electronics involved.
Setting them up
Mount both units firmly on the rail, zero them once at your usual distance with the windage and elevation adjustments, and write those settings down. If you ever remove the sights, check zero again after re-mounting. For reference, here is a listing for Ozark Armament flip up sights.
Using them alongside a red dot
The most common pairing is with a red dot. Raise the irons and look through the dot's window: if the front post sits right under the dot you have an absolute co-witness; if the irons sit in the lower part of the window it is a lower-third co-witness. Which one you get depends on the mount heights, so check it on your own rifle before counting on it. One example to look at is this red dot sight.
Practise flipping the sights up, and always follow local laws and range safety rules.