Have you ever looked at your keyboard and wondered why the ‘F’ and ‘J’ keys have bumps on them?
The raised bumps on the ‘F’ and ‘J’ keys are placed there for proper position of fingers while typing. For ease of use of the keyboard, these keys have ridges on them so that if you are speed-typing without looking at the keyboard a lot, then the ridges will help you position your fingers if in case you fly off the handle.
Positioning your left index finger on the ‘F’ key and your right index finger on the ‘J’ key leaves the other three fingers of your left hand to rest on the ‘D,’ ‘S,’ and ‘A’ keys while the remaining fingers of your right hand rest on the ‘K,’ ‘L,’ and ‘:/;’ (colon) keys. The thumbs of both hands should ideally rest on the space bar.
Source: f,j keya keyboard raise