When we create a db,the create command will create a data 
file with an Extension .mdf,as well as a transaction log 
file with extension .ldf
Any additional or secondary data files have .ndf extension

.mdf is extention of primary file,
.ndf is extention of secondary file,
.ldf is extention of log file,

sp_helpfile

sp_helpdb "database name"

For reading the log files (.ldf) an undocumented system 
stored procedure sp_readerrorlog is there.  This SP allows 
you to read the contents of the SQL Server error log files 
directly from a query window and also allows you to search 
for certain keywords when reading the error file.  This is 
not new to SQL Server 2005, but this tip discusses how this 
works for SQL Server 2005.

This is a sample of the stored procedure for SQL Server 
2005.  You will see that when this gets called it calls an 
extended stored procedure xp_readerrorlog.

This procedure takes four parameters:

Value of error log file you want to read: 0 = current, 1 = 
Archive #1, 2 = Archive #2, etc... 
Log file type: 1 or NULL = error log, 2 = SQL Agent log 
Search string 1: String one you want to search for 
Search string 2: String two you want to search for to 
further refine the results

If you do not pass any parameters this will return the 
contents of the current error log.

Example 1

EXEC sp_readerrorlog 6  

This statement returns all of the rows from the 6th 
archived error log.

Example 2

EXEC sp_readerrorlog 6, 1, '2005'  

This returns just 8 rows wherever the value 2005 appears.
Example 3

EXEC sp_readerrorlog 6, 1, '2005', 'exec'  

This returns only rows where the value '2005' and 'exec' 
exist.

Even though sp_readerrolog accepts only 4 parameters, the 
extended stored procedure accepts at least 7 parameters.

If this extended stored procedure is called directly the 
parameters are as follows:

Value of error log file you want to read: 0 = current, 1 = 
Archive #1, 2 = Archive #2, etc... 
Log file type: 1 or NULL = error log, 2 = SQL Agent log 
Search string 1: String one you want to search for 
Search string 2: String two you want to search for to 
further refine the results 
? 
? 
Sort order for results: N'asc' = ascending, N'desc' = 
descending

mdf: When You Create Database .this Primary file
ndf: This is Sceondry File
ldf: Lof Files