How to find the framerate I am playing the game at

You can try and download/install OptiFine, which is a mod for Minecraft that improves the performance of the game.

It improved my frame rate quite a bit after I installed it.

Note: This answer is mostly based on my personal experiences.

Higher framerate is usually useful, because games tend to run on a cycle where input is checked once per frame. The more input checks you can get per second, the less input delay there will be, and input delay is something that keeps coming up, especially in competitive games.

But keep in mind that some games use a frame-based timescale, which means that the speed at which events and animations play out depends on your framerate. Sometimes a higher framerate starts breaking the game engine and causing weird issues (like in GTA: San Andreas: swimming and vehicle handling break - or Dark Souls, where you might fall through the ground when using a ladder - or Need for Speed: Rivals where the whole game speeds up).

Also capping the framerate with vsync can cause stutters as the highest stable framerate changes (for 60Hz display, when the framerate drops below 60, the game will change the cap to 30). This is the main reason I go for uncapped framerate in games like Skyrim where the framerate can be anywhere between 40 and 100 depending on location and direction of the camera.