Well the rock looks better but it's little too dark for the coral I think. We need to find a happy median. To the users manual!! I want you to look up custom functions. I'm not sure if you are set to 1, 1/2, or 1/3 exposure stop increments, so lets make sure it is on 1/3.
C. Fn 1: Exposure - this should be the ticket. Choose "1/3".
C.Fn 2: Image - find "Highlight tone priority" and enable it. If you take a picture and your rock is all white with no detail, the preview in your LCD will flash the bad areas
Lets try f/5.6, ISO 400, 1/100
On your 18-55, you should see a series of switches. These will read something like AF/MF, Stabilizer On/Off, and Stabilizer Mode 1/2.
Select AF, Stabilizer On, Mode 1.
On your camera you should see a button, the illustration is a white square box with 5 squares in the middle making a cross. Push this and look through the viewfinder. Scroll through all of the red boxes until only the center box is lit up.
Press the shutter button down half way. You should feel the lens click and hear it hum, this is your image Stabilizer. Count two seconds, make sure you light the red box in a spot where 1/3 towards you will be in focus and 2/3 on the other side of what the box is touching will be in focus.