Check out some of the new screenshots showing the snapping feature. Snap lines are created by the intersection of the surface of the part with an imaginary plane. This lets you create any possible snap line and gives you total freedom to place parts how you like.
In other news the in depth tutorials for the game are nearly ready, so if you are an Alpha backer of this game expect to be able to test them soon.
This screenshot shows the creation of a snap line. The green snap line is an existing snap line while the red line is the snap line you are currently creating. You can set the snap line to any axis, then control its rotation or use the Auto feature which creates a snap line perpendicular to the face your mouse is hovering over.
Here you can see a wheel being placed on a main body that has had snap lines added. The wheel's position snaps to the line when your mouse gets close to it. It will also snap to snap line cross points. This lets you align wheels perfectly.
Snap lines, once created, are saved so you can use them on different levels. However you may not want them on all the time as they may get in the way, so you can disable snap lines that you are not currently using by toggling there visibility.
This last screenshot shows some of the flexibility you have when creating and using the snap lines.