Dynamic creating table in database in C#

"that means sir when new user sine up, c# create automatically database for that particular user."

That is a spectacularly bad idea! :laugh:
Creating a database or even a table for each user is a massive waste of space, memory, and time.

If you want a list of "contacts" which is specific to each user then create a table which holds cross references:
User Table:

ID      Name     Email
1       Joe      Joe@Domain.com
2       Mike     Mike@OtherDomain.com
...
1000    Fred     FredTheShred@RBS.com

Contacts table:

ID      UserID   ContactID
1       1        2
2       1        1000
3       1        777
4       2        1000
5       2        666

In this example, User 1 (Joe) knows user 2 (Mike), another user with the id 777 and user 1000 (Fred).
User 2 (Mike) knows Fred, and another user with the ID 666)
To find out which contacts a user has, you select the records from the Contacts table, asking only for those records with his User ID:

SELECT ContactID FROM Contacts WHERE UserID=1