( I underlined the important part the rest is extra info that can help you understand)
Answer
Lithium is a metal (Alkali metal) it will donate one of its electrons to fluoride so then it becomes positively charged (cation).
(atoms are neutral because protons (p+) and electrons (e-) are equal taking one electron from an atom will make it positive)
Flouride is a nonmetal so it will accept the electron from lithium so then it becomes negatively charged (anion)
lithium is in group 1 so its charge is +1
Flouride is in group 17 so its charge is -1
both cancel each other so there are no subscripts