The moving parts on your Ultimaker require lubrication like any other machine. Different parts of the machine require different substances. Applying the wrong substance can impede the function of your machine.
You received a tube of Magnalube (green grease) in your accessory bag. This grease is for the z-screw only. The z-screw is what moves the bed. Apply the grease and work it into the threads of the screw. If you see debris on your z-screw (dust, dirt, filament), wipe the screw clean before applying more grease. We recommend cleaning the Z-screw with alcohol and a lint free cloth as paper towels can shred on the Z-screw, creating debris. A dry z-screw can cause irregularities in your prints.
The X/Y axis (rods and crossbars that move the hot end) and the z-shafts (vertical metal shafts through the bed) use sewing machine oil for lubrication. Dust can mix with the oil on the rods. This build-up is usually visible at the ends of the rods where it has been pushed and deposited by the moving parts. Wipe the residue off as part of your regular maintenance. Avoid build-up by using oil sparingly. You do not need more than one drop of oil on any one rod. If your printer is moving smoothly, you do not need to add oil.