First you need to setup a Linqer Connection.

Linqer Connection Pool screen will be shown when you run program for the first time.

Click Add button to create a new Linqer Connection.

Specify a Connection Name (for example Northwind).

Specify a Connection String to connect to a SQL Server database.

If you already have a Visual Studio project with LINQ to SQL classes you can specify paths for *.dml and *.designer.cs files.
You can also generate these files using SqlMetal tool by clicking Generate LINQ Files button.

Specify a Data Context Variable, which can be used in the produced LINQ statements.

As soon as you setup a Linqer Connection you can convert SQL to LINQ.

You can have more than one Linqer Connection and pick the
active one from the Connection list on the main toolbar.

You can type, paste, or load a SQL statement from file into the SQL window.

Click F5 or use convert button  to produce a LINQ statement.

Click F7 or use Run button  to compile and execute LINQ statement.

The query result will appear in the bottom section of the screen.

You can look at the output SQL, which has been produced by the LINQ to SQL engine.

Code for DataContext variable declaration can be obtained at the Data Context section.

Click F6 to or use compile button    if you don't want to run a LINQ statement, but just want to make sure it is valid.