ArcGIS shapefile files are composed of mandatory files (SHP, SHX and DBF) and optional files (PRJ, XML, SBN and SBX). This article lists their functions.
The USGS Earth Explorer is quick and easy to download free Landsat imagery & other remote sensing data. Enter ROI, define timeline and download for free.
Some of the best GIS weather data available can be found at NWS, PRISM, MADIS and Weather Source. This GIS weather data dates back from past to present.