How to achieve the fabric you want: Stockinette vs Garter
So, you're knittng a cardigan. The body of it is worked flat; the sleeves, in the round. At some you are instructed to work in stockinette for some number of inches on both the body and the sleeves. To achieve the stockinette fabric, you will not always work the same stitch pattern, it will vary based on whether you're workng flat or in the round. This simple graphic will guide you in determing how to achieve the fabric you want [B-T-Dubs, K means knit and P means purl].