A Process is a unit of a series of actions by a program. Sometimes a process contains a very long series of actions. Nowadays, your computer and smartphone runs more than 50 processes at a time.
CPU can run very quickly, but CPU can do only a small thing at a time.
So, every process is further divided into threads (a minimum unit to do something), and each thread is further divided. CPU works on each part of threads of processes at one time