Basically, the difference between 4 season tents and regular tents is that a 4 season tent is tighter, with heavier and tougher outer walls. When it is all zipped up, there is no space anywhere for the ruthless natural elements to get in and disturb your peaceful sleep. In addition, 4 season tents are often more durable so that they can shield you safely from extremely heavy storms if need be. This does not mean, however, that you cannot use 4 season tents in more pleasant weather. Many styles of 4 season tents come with the option to unzip the outer fly so that you can catch cool breezes on summer days, while still being able to endure Ice - Age -type of temperatures in the winter.
Basically, the difference between 4 season tents and regular tents is that a 4 season tent is tighter, with heavier outer walls. When it is all zipped up, there is no space anywhere for the elements to get in. In addition, 4 season tents are often stabler so that they can resist extremely heavy storms if need be. This does not mean, however, that you cannot use 4 season tents in nicer weather. Many styles of 4 season tents come with the ability to unzip the outer fly so that you can keep cool on summer days, while still braving near-arctic temperatures in the winter.
You will find, however, that the more extreme the conditions for which it was designed, the more specialized a 4 season tent will be. For example, some true mountaineering 4 season tents are not things I would advise you to bring for camping on a warm summer night. The ventilation panels are narrow and the end result is that it will be stuffy and hot at night if you are camping during the summer with them. Additionally, they are made of heavier, stronger stuff, and as a result are an added weight for your normal camping trip in which lightness is a virtue.
And of course, good 4 season tents can come at exorbitant prices, running up to $500 dollars and more sometimes. Compare this to an ordinary 1-2 person summer tent that you might grab at your neighborhood camping store. I got mine for a tiny sum of $30 dollars and, although it provides little warmth, it gives me all the comfort I need during the summer when combined with a decent sleeping bag.
The truth of the matter is, it is important to think about what you will be doing before you go out and buy expensive mountaineering equipment and 4 season tents that you will not need. You must make sure that your equipment fits its purpose.