Dota 2 betting odds often work the same as traditional sports betting. The most common form of odds that are presented by sportsbooks is fractional odds. This is when odds are separated by a slash (/) and it displays how likely an event is going to happen through probability. So, for example, 9/1 can be calculated as 1 / (9+1) = 0.10 which means there is a 10% chance for that outcome to happen. This means that if you bet $1 at 9/1 odds then you will win $9.
The other most common format for odds is decimal betting. A decimal odd of 9.0 is calculated as (9.0 x a $10 stake) = $80 in winnings. People often find decimal odds easier to calculate than fractional odds. Once you understand the way odds work in traditional sports betting, you essentially understand how it works in Dota 2 betting.