If you want an introduction to more basic branch predictors that TAGE evolved from I highly recommend this:
https://www.ece.ucdavis.edu/~akella/270W05/mcfarling93combin...
It's old, but very clear. I tried to read the ITTAGE paper but it assumes you know all that already. Also it doesn't actually fully specify a branch predictor because there are various hashes you need to calculate and it simply doesn't say what they use.