Each Party publishes a platform explaining beliefs, principles and positions on issues. The National platforms can be found online:
Republican National Committee Platform (37 pages) https://prod-cdn-static.gop.com/docs/Resolution_Platform_2020.pdf
The Democratic Party Platform (92 pages) https://democrats.org/wp-content/uploads/2020/08/2020-Democratic-Party-Platform.pdf
Biblical Voter provides side by side comparisons on important issues: https://www.biblicalvoter.com/major-party-platform-comparisons/
State Parties that have Platforms generally get updated through a bottom up process through Precinct Conventions, County/SD Conventions, and the State Conventions. This Webinar series provides information on Conventions, Resolutions, and Delegates:
Webinar #1 - Conventions https://vimeo.com/protectingthegift/usingpartyplatforms?share=copy
Webinar #2 - Resolutions https://vimeo.com/protectingthegift/usingpartyplatforms2?share=copy
Webinar #3 – Become a Delegate https://vimeo.com/protectingthegift/usingpartyplatforms3?share=copy
Get involved and participate in the Party Platform process in your state!