Singles (2 Comb) is a type of accumulator.
It means if your have like 2 events on 1 bet slip, instead of the normal accumulator which multiplies the odds of the 2 games to get your odds product and then multiply the odds product by your stake to get your winnings, singles (2 comb) would multiply your stake by the odds of each of the 2 events individually.

Lets say you have Match A and Match B and you stake N100 on the entire odds (for the normal accumulator).

In singles (2 comb), Matches A and B would be on your slip but the stakes will be calculated individually for each match.
So if you enter N100 in the stake box, your total stake will be N200 meaning you will be charged N200 if you proceed with that bet, this is because you are placing a singles (2 comb) bet and your total stake will be calculated at N100  for each of the 2 events.
Unlike the normal accumulator, you don't have to win all the bets on the slip to get returns.

If you win match A then lose match B, your stake of N100 for match A will be multiplied by the odds for match A and you will be credited for that, you wont be credited for match B because you lost it. In singles (2 comb), there is no odds product.
Each event is staked on individually and winnings are credited individually for each event

An example of a singles (2 Comb) bet is displayed in attached.