A very thorough overview of everything you need to know for the 2020 election from the Committee of 70.
Voting information and resources for the state of Pennsylvania: https://www.votespa.com/Pages/default.aspx
Register to vote with the city of Philadelphia: https://www.philadelphiavotes.com/en/voters/registering-to-vote
Apply to vote by a mail-in ballot with the state of Pennsylvania: https://www.pa.gov/guides/voting-and-elections/?fbclid=IwAR2pb2NlASYH0-lTSf-Rs3ZoLyGIiNwavVlFTm6EAaW6iaWfVL_iVrJoNCc#VotingbyMail-InBallot