In: Computer Science
Requirements and specifications are the 2 main pillars of any project or any type of work flow. They are the building blocks of any task. Requirement means something required or wanted whereas specification means details anything particular, or as we can say detailed description of anything it can be a design, material anything.
The difference between them is requirement is something you want it'll be materialistic or specific like book, a laptop etc whereas specification is the detailed description of anything it can also be the description of the requirements as well. For example to setup a lab the requirements will be chair, laptop, table etc and the specifications will be softwares on laptop, design of chair and tables etc.
They are so important because they are the basic necicity in any task. If you have to start work on anything in any feild you first have to know what you want to do and how you want to do and that covers the requirements and specifications section. If you don't know what things and information you want to start your task you can't do anything.