[RM2K3] CAN'T FIND TUTORIAL!

Common events let you make many systems that affect to all game.
Btw you need any idea to make something.

Here's a few more things.

Common events are like functions in coding, they are a way to load a procedure.

They have three advantages of this:
1. If you have a process that is frequent (hence the name), it saves you the trouble of copypasting a local event over and over again.
2. More importantly, if you just copypaste local events, and you make an error somewhere, a common event, you can just modify inside the event. A local event you will have to edit EVERY event. This makes it the difference between a finished game and an abandoned one.
3. If something needs to be self-contained like three or four actions involving switches, when you are inside condition branches that rely on those being on, common events keep open until you exit them with End Event Processing. This is very very good because it prevents the branch from falling apart.

Other things to note:
1. It is highly recommended that you use common events for any math equation longer than about 5 or 6 lines. Not only will this allow you to edit it easier, but it seems like the processes operate separately from the opens in local events. This means that while event-heavy local events will slow on math crunching, common events will do it in a fraction of a second (it's processing using a different system).
2. Common events have different processes than battle events. This can work to your advantage or disadvantage, because it means common events can run things that aren't normally accessible through battle. However, this also means you can't put stuff specific to battle events (like Change Monster HP or variables of monster stuff) into common events.
3. Lastly, there are some times where common events won't work. As I've explained, battle events don't translate well. Movement ThisEvent also tends to cause an event not found error (basically, because common events are handled in a different "place" than local events this is probably what causes the fail). Because End Event Processing typically needs to be used to exit common events (unless switch-based) this means for stuff like exiting out of a local event cannot be done because the End Event will only exit out of the common event, not the local event that contains it.

Fortunately for you, many of the limitations of RM2K3 are done away with with the upgrade to official version. I believe common this events work, and copying of battle events to the common event section. This allows you to bypass some of the issues with common events not running certain things. But you still have to be careful.

4. Having stray common events can sometimes result in things like calling a common event in a loop (game crash, cuz it won't resolve), sharing an event with others in a nested common event, or having a switch-operated common event shut off a switch, but other events keep shutting the switch that operates the common event back on. Or you can have a switch common event where the switch is held by two common events. These latter three won't crash the game but they will create serious lag. You should also occasionally put a wait command on any parallel process events if they have to repeat (like stuff to track your location or check terrain).