Yes & no Paul.

I'm guessing that your pretty much a beginner by your statement that you weren't really sure what the %'s meant.
Learning the % are the basis of bookmaking & punting. Learn them and how they work.

Betfair SP lays to liability so different prices have different bets & different payouts. Every race market is structured differently, so laying for different amounts is crucial. I try to risk every favourite for a similar amount, (1 risk unit) which is only really possible if you wait until the last minute before betting. Laying earlier in the evening as I do is not perfect as horses tighten and drift which may change the possible results, but it's swings & roundabouts.

At the moment I'm averaging a profit of 5 (risk) units per night.

When I eventually attack the US markets I'll be flying pretty much blind but 9 times out of 10 the SP fav will be the only loser, only for differing amounts each race.