2NaOH + H2SO4 ==> 2H2O + Na2SO4
Equations like this are balanced by inspection which in simple terms means trial and error. You learn how to do these by practice; the more practice you get the better you become. Here is the process I go through.
NaOH + H2SO4 ==> Na2SO4 + H2O
The first RULE to remember is that you MAY NOT change any of the subscripts; you may change ONLY the coefficients.
I look at the equation and I see 2 Na atoms on the right so I know to make 2 Na atoms on the left like this.
2NaOH + H2SO4 ==> Na2SO4 + H2O
That makes Na ok. The SO4 is ok so I won't bother with it. For H I count up what I have on the left side and make the right side equal to that number. I see 2 H atoms from 2NaOH and I see 2 H atoms for H2SO4. That makes 4 H atoms on the left and can get 4 H atoms on the right with 2H2O.
2NaOH + H2SO4 ==> Na2SO4 + 2H2O
How do you know it is balanced? You ALWAYS check it.
I see 2 Na on the left and right.
I see 6 O atoms on the left (2 from NaOH and 4 from H2SO4) and there are 6 on the right(4 from SO4 and 2 from 2H2O).
I see 4 H atoms on the left (2 from 2NaOH and 2 from H2SO4). There are 4 H atoms on the right from 2H2O.
Don't get discouraged. This will come along with practice.