Connect Infopath form controls to SharePoint List data

Please go through the screens. It's very much self explanatory 

Above is the List view in sharepoint

In Infopath Designer, create an Infopath form and put on designer surface Drop-Down List Boxcontrol, click on it and press Alt+Enter to open it properties.

There, under Data tab, against choose "Get choices from an external data source" and press add press "Add..." button against "Data Source:"

Starting data connection wizard for Drop-Down List box in Infopath Designer 2010

Note that data connection can be created separately by a dozen of variants

Step2 of Data Connection Wizard "Select the source of your data"

Step3 of Data Connection Wizard "Sharepoint site details"

Step4 of Data Connection Wizard "The Sharepoint site site that you slected has the following lists and libraries you can use as your data connection"

Step5 of Data Connection Wizard "The Sharepoint list has the following fields you can can select from"

Running it:

Running Infopath form with Drop-Down List Box linked to a column ClientList of ClientList list

Hope this helps..