WPF Controls referencing in C#

Question

Well first of all, sorry if my thread subject is confusing -- because i am. Anyways I have a project built in WPF just for the better UI, and it is built in Windows Expression Blender 2. ( Don't know the difference between MSV2008 WPF and Blender besides the fact extra controls/features/etc ) Ok now to the point, I was wondering how would I reference WPF controls in C# code. Say I have a textbox control in WPF how would I reference what was typed in the textbox in C#? And the texted typed in WPF textbox control will be used for whatever needed. Thanks~