SQL Server - Select columns from Two table

 I have Two Tables 
Table1 have the Following Field

Employee Name
EmployeeID
Table2 have the following Fields

Requestedby

Approved by

I want to get the name of Requestedby and Approved by by join query How to do

select a.ColumnA, a.ColumnB, b.ColumnA as ColumnC, b.ColumnB as ColumnC
  from tableA a 
  LEFT JOIN tableB b on a.SomeKey = b.SomeKey
  where a.ColumnD = some condition
    and b.ColumnE = some other condition

What is the common field in both the tables??

Select a.employeename,
       a.employeeid,
      b.requestedby,
      b.approvedby
from table1 a inner join table2 b on a.(commonfield)=b.(commonfield)

Requestby,Approvedby are EmployeeIds.Thank u for ur Reply