It is a Samsung Model SGH-S275R and I am using the button at the side that usually turned my phone off or on THANKS
Welcome to the community!
On most non-smartphones, you press & hold the end call button to both turn on and turn off the phone.
Taken from Samsung S275 user manual here.
The button on the side of the phone is the short-cut to access the camera (as you already found out).
Hope this helps