Cools
I'll just go through the question with the example method they've outlined (there are lots of methods to balance equations, you might find another easier).
Step 1: Write down what you're told
HBr + H2SO4 ---> Br2 + SO2
Step 2: oxidation changes
You are told to balance
any atom that changes oxidation number so:
2H
Br + H2
SO4 --->
Br2 +
SO2 (now S and Br are balanced, but H and O are not)
now compare the oxidation states
2HBr + H2
SO4 ---> Br2 +
SO2
Sulfur has gone from +6 to +4 (reduction = -2)
2H
Br + H2SO4 --->
Br2 + SO2
bromine has gone from 2 x -1 to 2 x 0 (oxidation = +2)
Step 3: Balance oxidation changes
Nice and easy this time, they already balance
Step 4: Clean up
2HBr + H2SO4 ---> Br2 + SO2
two extra oxygens on the left, 4 extra hydrogens - add two waters to the right
2HBr + H2SO4 ---> Br2 + SO2 + 2H2O
That help?