The lagoon Nebula is the bright object in the lower right part of the photo. Located some 5,700 light years from earth in the constellation Sagittarius. It is formed from hydrogen gas that is excited by two stars and glows deep red. A little lower and left of the brightest part of the gas is a loose cluster of stars (NGC 6530) that is not actually part of the gas cloud.
In the upper left hand portion of the image are two objects. The first is the Trifid Nebula. This nebula is interesting because it actually is composed of four different astronomical objects. The first is a red "Emission Nebula" cause by excited hydrogen gas. The second is a "Reflection Nebula" which is the result of light bouncing off of gas and dust particles resulting in the blue you see. The third is called a "Dark Nebula" which is gas and dust that blocks light from passing through it. The forth and final object is an "Open Cluster". These clusters are loose associations of stars that form about the same time from clumps of gas. They eventually go their separate ways but while they are young they remain close to each other.
The final object in this picture is another open cluster located directly left of the Trifid Nebula. The cluster, know as M21, is composed of about 100 stars.
To give a sense of the image scale, the Lagoon nebula is about the size of the full moon.