I'd like to learn about Eisenstein series so I started reading "On the Functional Equations Satisfied by Eisenstein Series"by Langlands. http://www.sunsite.ubc.ca/DigitalMathArchive/Langlands/pdf/Eisenstein-ps.pdf I'd like to go through the first few chapters.

I'm struggling already at Chapter 2 (where he goes through the background material basically) because I don't have enough Lie groups/Lie algebra background; at least this is what I think is the reason, I have only seen Lie algebra material over $\mathbb{C}$ and in the book it seems to work with some other field (I think $\mathbb{R}$) and stuff looks some what different...

I was wondering if someone who knows this book could possibly recommend me an alternative (perhaps easier) reference to study similar material or possibly a reference to cover prerequisite to go through this book. Any comments/suggestions would be appreciated. Thank you very much.