Level

You may not need this tool very often, but it can be awfully handy when you do. You use it to make sure that things are straight. A basic level looks like a plain ruler that with one or more little plastic tubes. These tubes are filled with a greenish or yellowish liquid and has two lines that circle around the middle. (The lines go the way that you'd tie a ribbon around a rolled up piece of paper.) Each tube also contains a bubble: you know that the level is aligned when the bubble in the tube sits between the two lines.

Most simple levels have at least a tube going east-to-west (which lets you know if the level is being held straight horizontally) and a tube going north-to-south (which lets you know if something is plumb i.e. not leaning to one side). Sometimes, there will be a tube set at an angle: 45 degrees, 60 degrees, etc.

Now, you might be lucky enough get access to a laser level. These emit a laser light: it "draws" a level line that you can see for hundreds of feet and is incredibly accurate. They're generally used for things like building the foundation of a house. If you happen to have one lying around that's feeling neglected, Spiky Mochi would sure love to take it home and see what he might be able to, er, make of it.