I have migrated DTM to Launch and it's working as expected. After migration I have to work on new implementation In this process do I need to create a Library? Else, will the setup rules will automatically move to the productions.
Every time you want to change something on Staging or Production you need to create a library and include the changes in it. Then build it for Development and then step-by-step move it to the right in the publication workflow.
In addition to the help from Andrey, you can also select a "Working Library" in the top right corner once you have createed at least one. Once selected, all changes for your login account will be automatically added to that DEVELOPMENT library without having to create a new one in publishing everytime. When ready to promote to Staging and Production you will have to go through the publishing workflow.