New to photoshop

[Sooner266]

hey everyone, i just got adobe photoshop and I was wondering how to take the water in (A) and make it reflect the clouds in (B). I can make it select the water perfectly.




i know how to use the subs. brush, but i don't know how to get it to move the part that its taking from reverse of what i'm doing, as in a reflection.
PLEASE tell how me how if you can make any sense out of this.

help would very much be appreaciated,  ???