There's a couple of reasons to give Kudos – it’s good for the community and good for the member who is receiving the Kudos! It helps identify great posts, when you're scanning posts you can see particularly good posts/threads that have a few ‘Kudos’.
Additionally, Kudos act as a way of recognising the time and effort someone has put in and encourages good discussion. The number of Kudos someone received also helps their community ranking.
It couldn't be simpler. On the bottom right of every post you will see a star with a number next to it, just click on the star and you'll see the number on the left jump up by 1, showing you've given the member Kudos. Easy.
In mobile view its a little different. The kudo button is located at the bottom of each post on the left next to the reply button, just click on the kudo button and you'll see the number jump up by 1, showing you've given the member Kudos. Easy.
Giving Kudos feels good, and if that's not enough, giving Kudos is built into some of the ranking formulas, so along with a whole bunch of other factors – it can help increase your rank and contributes to the person's rank who is receiving the Kudos, so not only are you helping others, you're also helping yourself!