An increase is simply adding a stitch to the knitting. Consider all of the ways you could create a new loop of yarn on the needle. This sampler shows a variety of increase methods and includes videos on how to perform them.
A quick and very easy knitting pattern, perfect for the new to knitting (If you can cast on, knit, increase, decrease and cast off, you can knit this beautiful Baby/Toddler Cardigan). Using Garter Stitch (Knit every row) it creates a reversible knit and the pattern can be knit for either a girl or a boy.