Segments enable you to define certain properties, people and actions and create a specific segment for them. It works just like a list, but more granular.There are 2 ways in which you can create segments:
Select the segments tab > and create new segment.
Select the all subscribers tab > Use the filter to create a defined list that you want to create a segment with.
If you have a list on another platform or have a data base with customer data, you can quickly add all those users directly to your email subscribers lists.Select the subscriber tab > Click more and select the import option ‘as shown below’Check the agreement info and click import now to start the process.