Single pointed knitting needles or straight needles are probably going to be the first type of knitting needles that you buy as a beginner and you can count on buying many more, in the future.
Most knitting supplies stores will carry the full range of needle sizes in at least two lengths. The 20 - 25 cm lengths are used for small items like knitting for babies or children and the 35cm length is used for adult garments or larger items.
The shorter the needle, the fewer stitches you can comfortably work, but you will find that the physical motions of knitting are far easier. If you are attempting to work in a confined space, like an armchair with a narrow seat and fixed arms, or on public transport, the shorter the needles the better.
But sometimes you will find that you have no option but to use the longer needles or to consider using a circular needle instead.
These needles are usually available in the full standard range of sizes, from 2.0mm to 25.00mm, but you might find that the very small and very large sizes may be a bit more difficult to come by.
If you are into specialty knitting, you might want non-standard sizes. In the past I have used size 13, 14, and 15 needles (in UK sizes) for making tiny toys for my mother's porcelain dolls using crochet cotton (ever seen a four inch tall golliwog?) and I needed to source the needles from a specialty store.
Those needles were very sharp and very fiddly to work with, but the results were fantastic. For non-standard sizes, you have the choice of hunting for them as I did or finding someone who can make them for you.
© andykleinphotography | Canstockphoto.com - Needle Collection
These needles are used for straight knitting where you knit one right side row, turn the work and knit the wrong-side row. (Knit as in knitting not knit and purl stitches!)
You would use these needles for knitting the pieces for most garments you will make. But if you are planning on making a large item like a shawl or a blanket, it might be a good idea to look into using a circular needle as they can accommodate a larger number of stitches than single pointed knitting needles.