Python geoprocessing tool for ArcGIS online

I am looking to create a geoprocessing tool using python in arcGIS 10.2 that will be used in the ArcGIS online web app builder. This will be my first tool for a web application and I would like some information/advice about how to use ArcGIS REST services and hosted feature services in a python geoprocessing tool. When creating tools for ArcMap I use the

arcpy.GetParameterAsText() 

code and then choose a parameter in the script properties window. Is there a specific line of code to use to get feature services and REST services and is there a specific parameter to use? Also how do I show the result in a web app, my intended goal is to save out the results as a pdf file at a user defined location or as a separate html page.

Thanks