For a new CRM setup or migrating to new servers you will need to know hardware requirements and the software required to run CRM.
Use the link below and ensure you change it to the correct CRM version. If you have one application and one SQL server you will probably find that the Web App server will be running the front end and back end roles and the SQL server will operate specifically as a SQL server. If you use two web app servers, one may be running as a front end and one as a back end server. You must take all of this into consideration before you can understand all of the requirements.