Installing MCreator mods
MCreator mods can be installed on both Minecraft client and server. You will need Minecraft Forge in either case.
Installing MCreator mods on client
MCreator mods need to have Minecraft Forge to work. Make sure to use the same version of Minecraft Forge as MCreator uses. You can find out the version of the Minecraft Forge MCreator is using by pressing on the version number in MCreator. The version will be listed in the "about window" that opens.
MCreator mods are installed in the same way as other forge mods. You simply put your mod into the mods folder. If you don't have a mods folder then make one in your .minecraft folder
If you have trouble installing Minecraft Forge, follow these instructions.
Installing MCreator mods on the server
Some of the mods may not work on servers, especially the ones made with an older version of MCreator.
If Minecraft server starts normally, you can use the same exported zip/jar file for the server. To install forge and your mod to a server, use this guide: http://www.minecraftforge.net/forum/index.php?topic=1976.0