In this model, each device is working on a specific layer e.g. router works on network layer and bridge works on Data Link layer. Now as a network support person, if there is a problem in the ping between two computers in a huge network, you can start checking that whether the first computer can ping to the router or not. If yes, it means that there is no any problem till network layer and there must be some issue in the devices or interfaces working in the upper level layers.
This way, the knowledge of layered OSI model helps us in troubleshooting a large issue by breaking it into small ones.Check out the image for knowledge of some of the applications and protocols arranged according to their functioning layer in OSI Model. OSI.gif