With simple tools, there are endless possibilities in Creation mode.
Create Mode is a reoccuring feature seen throught the LittleBigPlanet series. In Create Mode, you can create levels using the tools given to you. Created levels can be published to the Community Earth where other players connected to the Internet can start playing the level.
The mode is unlocked in the first LittleBigPlanet game by completing the first Story area, The Gardens.
Overview
Create Mode is where you are able to let your creative juices flow by using your tools to create objects and levels and then release them to the public to show off your clever creation skills. It is a mode accessed via the My Moon option in the Pod where you can create levels on one of several given spots then publish your finished level to get Trophies, friend requests, hearts, and good ratings.
You can also just create objects and save them individually or create a level and not publish it. The main idea is, just be creative in any way you can possibly think of.
Tools and Objects
In Create Mode, players are able to build levels using the hundreds of tools, materials, and objects available. In LittleBigPlanet 2, Logic components were introduced, and other objects were added that made creating levels easier.
LittleBigPlanet 3 introduced Adventure Craters, and also added additional logic tools such as the Object Saver, Broadcast Microchip, and Object and Character Animation Tweakers.
Tweak Menu
In Create Mode, tools (from your Tools Bag) and some materials/objects (from your Goodies Bag) have Tweak Menus. The Tweak Menu is like a settings menu for many tools, materials, and objects! You can open it by pressing 
while aiming the Pop-It Cursor at a "tweakable" thing.
In the thing's Tweak Menu, you can edit certain properties belonging to it. For ropes, strings, and other such connecting wire, you can "tweak" their tension, length, or, for some, make a duration at which it will rise and fall. For bolts, you can tweak their tightness, and for motor bolts, you can adjust the speed at which it will spin. For lights and special materials from the Goodies Bag, you can tweak their color and brightness.
In LittleBigPlanet lingo, it is called "tweaking" an object when you change it using its Tweak Menu (such as making an LED light the color red, or speeding up a motor bolt to make an epic race car). To learn more about the Tweak Menu, you can play the Create Mode Tutorials, or you can experiment on your own and learn what you can do. There are also plenty of great resources to learn more about tools, materials, and objects, such as YouTube videos and LBP forums.