ergeben here means something like "to result in" -- so vier plus vier ergibt acht would be literally something like "four plus four [i.e. if you add four to four] results in eight".

Your translation is correct, but its uncommon - most of the time people will say plus for plus in a mathematical way. You might encounter that people say your sentence. You could also encounter some other translations like Vier plus vier ist acht or Vier plus vier ist gleich acht etc..