Before the latest Steam beta update, players concerned with how many frames being displayed per second would have to rely on game-native counters or third-party programs. No longer do we need such affectations to see tiny numbers in the top left corner of our screens.
In order to use this handy new Steam feature, one has to be opted in to the Steam beta program, which can be done via the Steam client's settings menu. There's really no reason for you not to be opted-in. No one has died from the Steam beta yet, and the more people signed up the better the odds of survival become.
Go into the in-game menu, and click the box most likely to add an in-game FPS counter to your screen.
Hint: it's somewhere in the screen capture above.
Once you're done you can spend a half hour looking for a game that's not capped at 60 frames per second by default, then give up and use a screenshot of Construction Simulator 2015, just like the pros.