OpenGl Depth buffer

eg. Two triangles were drawn, 1st blue and 2nd red. these two triangles intercept each other.

1. if Gl depth buffer is not enabled, triangles will be drawn one over the other. So that the triangle which is drawn on top will be visible. Explanation from example: red will be visible completely.
2. if depth buffer is enabled, the triangle which is drawn 1st will be visible. Others were rendered behind it. Explanation from example: blue will be visible completely.