Hi,
I understand that declination is the degrees around the earth, like latitude, however I have been told that the declination of the sun at summer solstice is 23

The first is the degrees and the second is minutes.
Each degree is broken down into 60 arcminutes.

Minute of arc - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Arcminutes)
Declination - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Declination)
Latitude - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Latitude)

Remember that an object's declination is the number of degrees north or south that it is from the celestial equator. You can visualize where the equator is by first locating the north star (I am assuming that you are in the northern hemisphere) and then imagining a circle in the sky that would be 90 degrees to the south from there - that's the celestial equator. If you live in a moderate northern latitude the celestial equator is an arc that starts at the eastern horizon, rises up towards the south reaching a maximum altitude above the horizon as you look due south, and chen continuing on down to the western horizon. The maximum elevation of the equator above the southern horizon in degrees is equal to 90 degrees minus your latitude. Because of the tilt of the earth, the sun follows a path during the course of the year that is tilted to the celestial equator by a bit more than 23 degrees (23 degrees 27 minutes). So the furthest that the sun gets north or south from the equator is 23 degrees 27 minutes. The summer solstice is the time when the sun is furthest to the north of the equator (again, assuming you live in the northern hemisphere), on or about June 22, so that is when its declination is north 23 degrees 27 minutes. At the winter solstice the sun is at its furthest southern declination: south 23 degrees 27 minutes. At both vernal and autumnal equinoxes (March 22 and Sept 22, respectively), the sun is at 0 degrees declination, which means that's the point in time when the sun is on the celestial equator. Hope this helps.