Back up option > Will generate full database backup file with extension .bak and this can be used in another server where you can use Restore option, use the .bak file and have the DB restored in that another server
See step by step guide - https://video2.skills-academy.com/en-us/sql/relational-databases/backup-restore/quickstart-backup-restore-database?view=sql-server-ver15
Import / Export data option > With this option, you can export the data from DB, specify tables to copy or provide a query, select target DB and the data gets copied to target server/db.
See step by step guide - https://www.mssqltips.com/sqlservertutorial/202/simple-way-to-export-data-from-sql-server
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Please don't forget to Accept Answer and Up-vote if the response helped -- Vaibhav