Understand might be too strong a word, but I studied Islam extensively while writing my Master's Thesis, "The Effects of Islam on the Persian Civil Service." Spoiler alert: it wasn't good.
I agree with Bill Maher, who said that "Islam is a Pandora's box of bad ideas." While this can be said of most religions, Islam is particularly guilty of misogyny, homophobia and xenophobia, and has never experienced the kind of reformation that brought mainstream Christianity and Judaism into the modern world, or the late Middle Ages ar least.
This is not a blanket condemnation of all Muslims, most of whom are decent people. I am, if fact, sponsiring a Muslim refugee and her daughters. Nonetheless, the danger of Jihadist extremism is based on the basic tenets of a religion whose founder was a violent, sexually driven sociopath whose religious conservative followers take every word of his ravings seriously.
I could (and have) gone on for three hundred more pages. Instead I will refer you to the works of Ayan Hirsi Ali and Nonie Darwish, two women who grew up under Sharia Law and are far more capable of explaining just what it does. I will confine my short version of an answer to: "The main thrust of Islam is the subjugation of women and the extermination of all non Muslims, starting with the Jews."
Thanks for asking.