What do subscripts in a chemical formula indicate?

Answer 1

Subscripts indicate the number of the preceding element

Ie. in H2O there are two hydrogens (H) and one oxygen (O)

or in C6H12O8 there are six carbon (C) twelve hydrogen (H) and eight oxygen (O)

The number of atoms of the same element in the molecule

Answer 2

The subscripts indicate the number of units of either an atom(as ion), l or molecule(as ion- called a radical)

in a chemical formula.

A unit of water, H2O is a molecule consisting of two units of hydrogen and

one unit of Oxygen.

A unit of Barium Hydroxide is Ba(OH)2

and here, the 2 indicates that the OH unit is the hydroxide radical, literally a

water molecule that is missing one hydrogen atom and it combines, as

TWO units to 1 unit of Barium {omitted subscripts are actually the number 1}