Turning an image Grayscale (B&W) and Sepia

Option 1
Open your image (File -> Open)
Image -> Adjustments -> Desaturate

Option 2
Image -> Adjustments -> Hue/Saturation
Slide the Saturation slider all the way to the left or simply type in -100

To get a Sepia look
Image -> Adjustments -> Hue/Saturation
Tick off the Colorize option
Hue = 36
Saturation = 19

Depending on your picture, for either options, slide the Lightness slider to your liking