This is a bloody sea effect, you can also make it because this example has been step by step described.
Color settings: First of all select background and foreground color as given below.
New Document: Take a new file with any size as you like.
Clouds: Go to Filter menu > Render > Apply Clouds.
This will come out.
Increase size: Press Ctrl + T key and right click then choose "skew" to increase bottom portion.
This is your done.
Recommend the tutorial