Step 1: Gather Files
Drag a downloaded file into the model window of MakerBot's ReplicatorG software.
If you don't have a 3d printer, you can still have the files printed at a commercial 3d printer.
Note that if you have two extruders (the more expensive model), you can choose to use the left extruder (drop down menu item on first check box) if you so desire.
Select "Generate Gcode."
Step 4: Picky Stuff
About the 20th line down in the Gcode list is a line "M109 S100 T0" Change the "S100" to "S115". Choose "File, Save."
Keep the "gcode" tab selected.
Start the print by selecting the "arrow into the peanut" icon.
It can take up to three hours to print even the fairly simple parts.
Step 6: Leveling the Build Plate
How to level the build plate . . . . here's what I do. Go to "utilities, level build plate" (on the Replicator, not the computer). Tighten the four screws and start the process. Instead of using a sheet of paper, I "eyeball" the extruders and get them where there is barely daylight between the extruder and the plate. The mistake I made many times was not turning two screws at the same time (the instructions say to turn two screws, not one). For example, I would start in the first position raising the plate and the right extruder would touch. I would quit turning the right screw and adjust with the left--which usually didn't have enough play to work. My mistake. When the right extruder touches and there is air on the left, reverse direction on the right screw--lowering the right while raising the left. Always keep turning both screws while adjusting--not necessarily in the same direction. This seems to work better for me.
Step 7: Cool Air, Raft Release, Curling
Changing the rubber band, weight in the car and connection to the rear axle (if the rubber band is finger held instead of secured to the rear axle, the car can free wheel when the band is exhausted) can impact the distance traveled.