Above, this project is worked in rounds, and if you are doing a regular sc, the next logical place to put the next stitch is in the marked sc beginning the next round. But, we're not going to do that because we are working in reverse.
Above, instead of going into the marked st to the left, I am inserting the hook in the stitch just worked to the right. (working in the reverse....)
Above, just like a regular sc, I inserted the hook, yo, pull up a loop, yo and pull through both loops on hook. The only difference is where I put the stitch (to the right instead of to the left). Here is the first rev sc stitch completed.