What is the need of databasenameLog file c# sql.

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C#

SQL

database

I am making the backup of the database using SMO. i have created it's backup file, But i want to know that afetr creating it's backup( databasename.bak) should i also make databaseLog.bak file.What will be it's function.

Now i have just created the backup file ,and the when i restored it, in sql server 200 it's showing (Databasename....restoring) , Is it the effect of not making the log file.