Work even means to work in the pattern stitch without any incs or decs. Do that until your piece is 2½" from the cast on. 'Ending after a WS row' means that you work the WS row and the next row will be a RS row.
If you're doing ribbing, since both sides look pretty much the same, then just work to the measurement and the next row will probably switch over to stockinette st where you'll be knitting the RS row.
sue- knitting heretic