Knitting machines can make three basic stitches automatically. Each machine manufacturer, unfortunately, has their own set of settings and their own nomenclature for these stitches.
On this site and in the Fabulous Machine Knitting patterns, the stitch types are referred to as knit, tuck, and slip. We generally leave it to the knitter to translate these basic terms to the machine they are using.
A knit stitch is the basic stitch formed by the machine. New yarn sitting in the hook of the needle is drawn through the loop on the previous row of knitting. In hand knitting this stitch is called either a knit or a purl, depending on the direction you work it. In machine knitting, if you have a single-bed machine, the purl side of these stitches will be towards you. On double bed machines, the knit side will be towards you on one bed and the purl side towards you on the other bed.
The tuck stitch is formed when the knitting machine lays a length of yarn over the stem of the needle. This yarn is not knitted through; rather, the loop of the previous row remains on the needle. In hand knitting, tucks may be represented by yarn-overs (as in brioche knitting) or as knit-one-below or purl-one-below instructions. Several tucks may be accumulated on a needle before they are knitted off, or they may be knitted off after a single row, depending on the pattern.
The slip stitch is formed when the yarn passes under the needle, leaving the loop from the row below still on the needle. Slip stitches are used in jacquard (fair isle) knitting where first one colour is knitted and the other slipped, and then the reverse. The hand-knitting term is also slip.