Open the Apex Data Loader and Select Export

Enter your username and password.

The password is your usual password followed immediately by the security token:  PasswordSecurityToken

Click Login, and then once successful click Next

From the Select Salesforce Object

1) Select the Object you wish to export.

Then click Browse to locate where to save the file.   NOTE: you MUST enter the file extension .csv when saving the file to be able to use if for updating the records through the Data Loader.

Then click Next

You will now select the fields from the object that you wish to be present in the Export file.

1) Choose the query fields below.   In this section you can select any of the available fields to export.    At the very minimum we recommend the Id and Name fields.  The Id field will be need to perform an update on the exported records and the Name field helps to identify the records you are working with

2)  You can then select the clauses or filters for the query.

Fields:  Any fields available in the object

Operation: select from equals, not equals, less than, greater than, less than or equals, greater than or equals.

Value:  Enter any value that would be available or present in the selected field.  Can leave blank if you want records that either contain no information in that field (field equals blank)  or contains some information in that field regardless of what that information is (field not equals blank).

3) Once you've set the clause, click on Add Condition.   (Note: you can add multiple clauses/filters to your query one at a time.)

4) Once you have set the fields and clauses, click Finish.

You will receive a confirmation message to proceed.  Click Yes.

Once the file has finished uploading, you'll receive a confirmation message.  You can look at the error and success logs, or click OK to close the window and open the Error and Success logs from their saved locations.

You can now open the export file and make the necessary updates to the records and then use the Apex Data Loader or the data management tools in salesforce to update the records.

For a listing of the various posts on updating records/ data management, click here.