Cpu scheduling is a process that allows one process to use the cpu while the execution of another process is on hold( in waiting state) due to unavailability of any resourse like 1/0 , thereby making full use of CPU.

The aim of CPU scheduling is to make the system efficient, fast and fair.
Whenever the cpu becomes idle, the operating system must select one of the processes in memory cpu to one of them.

What are CPU burst time and I/O burst time?
CPU burst time is the amount of time required by a process or can be said the amount of time required by the process to finish. We can not estimate the time taken by the process before running it. So most of the problem is related to the burst time.
burst time: Turn around time(Completion Time) Waiting time
1/0 burst time: While the process is in the running state, it may ask for i/o which make the process goes to the block or wait state, where the i/o will beprocessed and then it will be sent back to the ready state.