To build your bridges you've got several different kinds of materials. Starting out you can use asphalt and wood, which let you construct basic bridges but don't have much versatility. As you beat levels, though, you'll unlock materials like steel cables and rebar.
Building a viable bridge for your vehicles isn't actually all that hard, which is why normally it will only get you one star. To get all three stars in each level you've got to optimize your resources, which is much trickier than it might seem. Especially considering that you've got a very limited budget for each level.
Build a Bridge! is a very fun puzzle game with more than 30 levels and good graphics to boot. The most fun thing about it is that you can switch camera views when vehicles pass over your bridge and see the action from loads of different perspectives, including first-person or 2D.
Requires Android 4.1 or higher.