Start with the straps set far apart from each other, so if you're doing them in the power rack, hang the straps from the sides. From there, grab the right strap with the left hand and the left strap with the right hand and row as normal.
These feel quite different from regular inverted rows, in a good way. With a regular inverted row you're pulling straight up, whereas here you're pulling up and out to counteract the straps trying to pull your arms inward. This pulling action makes for an awesome contraction, especially if you try to hold each rep at the top for a second.
These are definitely harder than regular inverted rows, so keep that in mind and make sure you've mastered the necessary progressions before trying them.