Select the Line Tool (N), and draw a line about 100 pixels long, at about a 30 degree angle. If you want to be precise, you can draw a vertical line of any size and set its height (H) to 100 pixels through the Property Inspector and then rotate it by 30 degrees using the Transform panel ( Window > Transform or CTRL/CMD+T):
Select your line. Then copy (CTRL/CMD+C) and paste it in place (CTRL/CMD+SHIFT+V) in the usual way.
While you hold down the SHIFT key, press the RIGHT arrow key a couple times to move it off of the previous line. Then select Modify > Transform > Flip Horizontal . With this line still selected, grab the top edge of the line and snap it to the top edge of the other line.
Select the Line Tool again and draw a line from the bottom of the first line to the bottom of the second line, thus completing a triangle.
Next, draw a line from the top of the triangle with the Line Tool to about 25 pixels above and 25 pixels to the right of the bottom right of the triangle.
Then, draw another line connecting the end of that line to the bottom right of the triangle. You're probably starting to realize the benefits of having View > Snap to Objects selected right now.
Fill the front of the pyramid with the main red color you've been using (for the record, it's #CE0000 ), and fill the right side of the pyramid with the secondary red that you used in the cube example. Finally, delete all the lines and you have a neat little pyramid.