There is no "correct" temperature for soldering. It all depends on a variety of conditions. You will need to adjust your temperature up or down as the soldering job changes. Remember that when you apply the iron to the job not only will the iron heat up the joints you are trying to solder but also that the iron tip will cool down also as it transfers heat to the joints. How much depends on the power to the iron, the tip size, the size of the items being soldered, how good of a heat bridge is formed between the various items, and the thermal conductivity of the items. Given all these variables, you can see how it's prettty much impossible to give a "one size fits all" answer. However, the general goal is the same. You need the iron hot enough that you can get all the parts to be soldered up to temperature in a a few seconds, but not so hot as to overheat the parts being soldered or the solder itself. If in doubt, start at a lower temperature and work your way up.
You want to use the lowest temperature which will let you form a good solder joint. You can tell a lot by how the solder performs as you try to make the joint. If the solder doesn't melt nearly instantly, doesn't flow smoothly, or only melts in the immediate area of the iron; the temperature is too low. If the solder gets dull and overheated almost immediately after touching it to the iron, or the circit board or other components discolor/melt quickly, then the iron is too hot.
Ideally, you should be able to touch the iron the the components to be soldered, apply a small bit of solder to form a heat bridge, then pause only a second or two to let the parts come up to temp. Then you should be able to continue applying more solder to form a hjoint and it should melt immediately and flow smoothly to cover all areas of the joint. The entire process should take no more than about 10 seconds. If it takes longer than that, you either don't have a good heat bridge between the parts or your temperature is too low. Likewise, if you see the solder or the components overheating in that same time, you have the iron too hot. Personally, I use the appearance of the solder itself to tell if the iron is too hot. If it's getting overheated quickly, I turn down the iron.
So much of this is hard to describe, but if you do a little practicing you should start seeing how the solder performs once the heat is just right. The symptoms of too little or too much heat are fairly apparent.
