What it does
The gdalwarp utility is an image mosaicing, reprojection and warping utility. The program can reproject to any supported projection, and can also apply GCPs stored with the image if the image is "raw" with control information.
How to use it
Add as much input files you want to warp.
Specifiy output format using short name (http://www.gdal.org/formats_list.html).
Specify source and target spatial reference set.
Advanced options and sources
To see complete details and help section please check the official gdal sources.
http://www.gdal.org/gdalwarp.html
Raster Processing Tutorial : https://trac.osgeo.org/gdal/wiki/UserDocs/RasterProcTutorial