I’ll let somebody else hit you with the theory and whatnot, but in my own journey pushing myself left I started with Zinn’s A People’s History and Loewen’s Lies My Teacher Told Me to unprogram all the crap they taught you in school.

Then while not necessarily leftist, to understand modern politics, I’d recommend Listen, Liberal by Thomas Frank and Dark Money by Jane Mayer noting that while Mayer pretty much gives the Dems a free pass, Frank points out that they were benefiting from the Koch brother’s antics right up until about 2014. MacLean’s Democracy in Chains is a good background on neoliberal’s origins and how they linked with the Koch brothers.

You can also give The New Jim Crow by Michelle Alexander a read, but honestly you could watch 13th and get the same understanding of the modern justice system’s racism.

Again, this all not necessarily Leftist, but it’s good for ripping the band aid off the lib shit we were taught.