How is fluoride created?

One way to make sodium fluoride is to react the hydroxide with hydrofluoric acid. The resulting salt can then be purified by recrystallization.

NaOH (aq) + HF (aq) = NaF (aq) + H2O (l)

While not a normal route of preparation because of the expense, sodium metal reacts vigorously with all the halogens to form sodium halides. So, it burns with fluorine, F2, to form sodium (l) fluoride, NaF.

2Na (s) + F2 = 2NaF(s)