Get dates of the MSSQL Database Transaction Log records
Your question is not very detailed in exactly what you want, but How to read and interpret the SQL Server log has some very good information about interpreting the SQL Server log.  

Specifically relating to finding the start of a transaction (from the above post):


  The first think I will do will be to look at the LOP_BEGIN_XACT
  operations. This log record marks the beginning of a transaction and
  is very important in log analysis because is the only log record that
  contains the date and time when the transaction started, and also
  contains the SID of the user that had issued the statement. Here is
  how I query for these operations:


select [Current LSN], [Operation], [Transaction ID], [Parent Transaction ID],
    [Begin Time], [Transaction Name], [Transaction SID]
from fn_dblog(null, null)
where [Operation] = 'LOP_BEGIN_XACT'