http://www.revenue.pa.gov/FormsandPublications/FormsforIndividuals/PIT/Documents/pa-40g-l.pdf
Or are asking how to get a credit for taxes paid to another state within Turbotax. If so, go through the PA interview, you will be asked if you paid taxes to another state, say yes.
Be careful. PA has reciprocal agreements with NJ, MD, WV, OH, VA, and IN. If you had wage income from any of these states, PA will disallow the use of Schedule G.
