a) Every SQL SERVER has a master database.
b) It contains special set of tables which keeps track of the system as a whole. It means it keep information about the new databases as well as all the objects in all databases.
c) This database is very important our system.
d) This database cannot be deleted.
a) It is a template for creating a new database.
b) We can alter this template.
c) We need to keep many things in mind in order to alter the template Db eg.Size of the model DB cannot be smaller than 100MB.
a) It the place where SQL SERVER agent stores there system tasks.
b) Eg of tasks could be schedule backups , schedule sps etc. One you create a schedule an entry is made in the msdb database.
a) This DB is used to help temp data like temp variables.
b) It is also used to hold things temporaily eg. consider you have a complex query and system needs to build in between a table so it saves the same at the tempDB.