The simplest Dutch would be in a game with only 2 outcomes (eg tennis) where only player A or Player B can win.

If they were equally matched then the odds on each should be 2.0. Therefore if you bet £10 on player A and £10 on player B, whatever the outcome you would win £20 at 1 bookie and lose at the other making it a no-loss match.

If the odds are lower (eg 2.0 at 1 site but 1.9 at the other) they you need to adjust the stakes to get equal outcomes and will lose money - you will get 1/(1/2.0 + 1/1.90)=97.4% of your money back.

If the odds are higher (eg 2.0 at 1 site but 2.1 at the other) then you will get a profit back equal to 1/(1/2.0 + 1/2.1)=102.4% of your stakes.

You can do the same thing with 3,4,5 etc way matches although these are much harder to spot. Although Andy will disagree, as dutching calculator is handy for these. You can find several but an easy online one is at oddschecker - click on the 'powertools' drop down box at the top right.

As Andy says - find some odds and post them and someone can show you how it would work