Similar to "Liking" a post on Facebook, Kudos are a quick thumbs-up you can give to your fellow athletes to congratulate them on a noteworthy activity, an achievement, entering or completing a Challenge, Race, or Goal, etc.
Interacting with Kudos on Strava through the Android app.
From your activity feed, you can see how many Kudos an activity has already received, as well as giving more Kudos by tapping on the 'thumbs up' button. Activities for which you've already given kudos will show this icon in orange.
From an Activity page, just tap the Social bar to view and give Kudos - this will take you to the Social view for that activity. From this page, you can give kudos by tapping the 'thumbs up' icon or see a list of athletes that have already done so by tapping the row of their profile pictures. You can manage your Notifications regarding Kudos from the Settings menu in the Android app, within the Notifications section.
Can I "undo" or delete a Kudo I gave?
There is currently no way to remove Kudos once they have been given... That wouldn't be very sportsmanlike!
Can I give a Kudo more than one Kudo at a time?
Due to a few bugs with the Kudo "bomb" feature, it has been disabled for the time being.