How to write chemical equations from word equations?
Like compounds like Sodium Chloride

You need to know the valencies of the concerned elements. Sodium has valency one, and so does chloride. Then you sort of 'cross multiply'.

\text{Na\\ \,\searrow \\ \,1\\Cl} \,\,\,\,\,\,\,\text{Cl\\\swarrow \\ \,1\\Na}

That gives NaCl

Now, say, calcium fluoride. Calcium has valency 2 and fluoride valency 1.

\text{Ca\\ \,\searrow \\ \,2\\F_2} \,\,\,\,\,\,\,\text{F\\\swarrow \\ \,1\\Ca}

That gives CaCl_2

Now iron (III) oxide. Iron valency 3, and oxygen (from oxide) 2

\text{Fe\\ \,\searrow \\ \,3\\O_3} \,\,\,\,\,\,\,\text{O\\\swarrow \\ \,2\\Fe_2}

That gives Fe_2O_3

Is that OK?

Thanks Very much.

But what is meant by, terms like nitrate, ammonium, sulfate

Nitrate, like ammonium and sulfate are salts.

Nitrate is NO_3, ammonium is NH_4 and sulfate is SO_4.