You need some foundational training about ISO 9001:2015 to understand the language, for you and for a core Project Team. The first step is to perform a Gap analysis, to determine the amount of work to be done - comparing what your organization already has in place versus ISO 9001:2015 requirements. From that GAP Analysis, you can develop your Project Plan, listing what needs to be done, by whom, until when.
Then, an important step is to design a model of how your organization works as a set of interrelated processes: Your organization has any research? Develops new products? Looks for customers, sends proposals, wins orders, prepares, and delivers those orders. Buys products, tests those products, and warehouses them. Trains people, keeps the work environment and equipment. From there you go to implementation in order to close the gaps found. Then, perform an internal audit and the management review. There you can decide if your organization is ready for a certification audit.
This is a very short description of the journey but below you can find more detailed information: