Photoshop :: Pictures And Text - How To Add/edit/remove/etc

lets say i have a picture. I want to add text to it so it fits right into the background rather than having an artificial white border around the text. How do i do that?

Also, how do i remove text without deleting parts of the background as well, and how do i enter text so that it matches the text that is used in the picture?

Lets say i have a picture with the word "TEST" in it, with a certain font, size, color, etc. I want to add additional text with the exact same font, size, etc.