Stretching

I'm 24 and I'm trying to stretch my body. Who knows if I could=) It's pretty easy to stretch my legs, but my back... Uuhhh... It's like a rock! My back is not flexible at all! I will be so really happy if someone who'll read this could gimme an advice how to stretch my back. What  physical exercise could be nice for it? Pleaaaseeee=)

xoxo