System bet – is a sequence of accumulators each combining an equal number of outcomes all based on a particular set of events. It is not necessary all outcomes to win in order to get winnings. 

You need to select size of the system bet, for example 2 from 3. It means that there will be formed combo bets, each combo has 2 event from 3 selected ones. In this size only 3 combinations are possible. 

Event_1 and Event_2 
Event_1 and Event_3
Event_2 and Event_3 

Let's assume that this events have following odds:

Event_1 = 1,2
Event_2 = 1,3
Event_3 = 1,4

In that case odds of the combination will be as shown next:

Event_1 and Event_2 odds are equal to 1,2x1,3=1,56
Event_1 and Event_3 odds are equal to 1,2x1,4=1,68
Event_2 and Event_3 odds are equal to 1,3x1,4=1,82

Asume that bet stake is 600. Bet stake is divided equally between all combinations. For each combination bet stake equals 200. If 3 events win, then 3 combinations will win. In this example bet winning will be defined by the following way: Bet stake for each accumulator (200) is multiplied to combination odds, then all bet stakes of all combinations is summed up.
In our case:

Event_1 and Event_2 odds are equal to 1,56x200=312
Event_1 and Event_3 odds are equal to 1,68x200=336
Event_2 and Event_3 odds are equal to 1,82x200=364

Winnig amount is 312+336+364=1012

You can choose different size of system, besides this one. If all selected events win, You will get Maximum win. If not, all the events did not win in the system, and part of the combo loses, therefore, the winning amount in the system can be less than the amount of bet. If won events less than selected size of the system, as in example less than 2 from 3, then bet will lose. 

If you have questions about payment, You can see Visual "system" bets calculator by clicking the word System bet in Terms and Condicitions 3,3. Enter the data according to your bet and You will see visual table of your bet with full calculations. 

In our case we have: 

Total winning amount: 1012