My question is about the correct order to read the papers by Arthur on trace formula. Arthur's papers are perfectly well-written, but maybe a little too hard for me to go through easily.

I would like to start with unrefined trace formula, but there are bunches of papers already. There is a paper on trace formula for rank-1 groups (1974), and there are two papers on trace formula for general reductive groups (1978 & 1980). Also there is a paper in Corvallis Proceedings (1979), and a notes on trace formula (2005) which has become the standard introductory notes on this subject. I am seeking for any advice on how to read these references.

I wish to at least go through some details to feel how the formula is proved. Now I have read the notes by Whitehouse on trace formula for GL(2) (which covers a great many details about computation), and read a small part of Arthur's paper on rank-1 groups (1974). My question is that whether it is better to take 1974 paper first to gain more intuition, or instead start with the more general setting of reductive groups (like 1978 & 1980 papers), where maybe things are actually more clarified.

Any recommendation of other references is also sincerely welcomed. I am not aware of any other introductory references on trace formula on general reductive groups.

Thank you very much for reading this lengthy question! I am totally new to this community, so you are welcomed to point out any mistake.