So this means they used the mpMRI to take targeted samples from the right side area identified on the MRI, and 4 out of 4 of those were positive. They also took 2 random samples and 1 of those was positive. Left side was all clear.
PSA density is a PSA value corrected for size of your prostate (e.g. larger prostates will produce higher PSA, but that in itself isn't an issue).
IPSS is the score from the IPSS questionnaire you filled in about the state of your waterworks (how often you get up for a pee in the night, how often your pee stops and starts again, etc). It's really aimed at people with Benign Prostate Hyperplasia (BPH), but it's useful for Prostate Cancer too, and in addition to what issues you might have, it gets your feeling about if they bother you or not (would you be happy to live the rest of your life like this?).
Did you get a T score too? Probably T2a or T2b?
My guess is you'll be offered prostatectomy or seed brachytherapy, and you'll need to choose which.