Hm... I think what's going on is that you increase as directed for row 3, then every following 4th.
What that second paragraph looks like it's doing is recapping what you've just knit for row 3 ("1 st at each end of 3rd") then giving instructions for what's to follow (every next 4th row). So, on that third row, you will have added 2 stitches. Every following 4th row, you will add 2 stitcehs. Go until the listed number of stitches.
R1 - knit as directed
R2 - knit as directed
R3 - increase 2 stitches, one at each edge, as directed
R4 - knit as directed
R5 - knit as directed
R6 - knit as directed
R7 - increase 2 stitches, on at each edge, as directed
Repeat Rs 4-7 until destired number of stitches.