If you're talking at the literal baseline "What opens a .shp file?" then the answer is to put them into any GIS program, with QGIS being the most popular choice. PDF related and Datapolitan.com are good for bare-basic tutorials that keep it under 300 pages. The more theoretical "What do I do with this data?" is a lot harder, since you're diving straight into the intelligence process at that point. I've found the biggest problem is identifying questions, but once you finally do then it's just a matter of hunting down applicable data and learning which tools answer the question the best.