All of the geoprocessing tools can be setup in ModelBuilder within ArcGIS. Once in ModelBuilder you can export the code out as python. To run the code you can either right click it in Windows Explorer and run it with python.exe or copy the code line for line into IDLE (Python GUI), which is installed with ArcGIS.
# Import arcpy module
import arcpy
# Local variables:
point_shp = "C:\\temp\\point.shp"
# Process: Add Field
arcpy.AddField_management(point_shp, "NEWFIELD", "TEXT", "", "", "25", "", "NON_NULLABLE", "NON_REQUIRED", "")