People often confuse knitting and crochet. It's understandable that this happens; these crafts share many similarities and common elements:
Some knitters – hand knitters, that is - use pointy knitting needles. The pointy needles can appear in several different types of configurations; they often exist in sets of two, although this is not always the case.
Hand knitters are only a subset of the total number of knitters; in addition to hand knitters, there are also loom knitters and machine knitters. There are many different types of looms and machines that can be used for knitting; they range from the simple to the complex, from the small to the large. Some small machines can be used to knit i-cord, socks or various other small projects. There are larger machines that can be used to knit sweaters, garments or other similar projects. Then there are huge circular machines, some of which wouldn't even fit in the living room of an average home, that are used to mass-produce knitted fabrics for the garment industry.
Knitting machines facilitate the production of knitted fabrics from very fine threads and yarns. For example, t-shirt fabric is usually knitted; because crochet must be done by hand, and it's tedious to use such fine threads for crochet work, it's rare to find crocheted fabric as lightweight and "drapey" as knitted t-shirt fabric.
So, to recap, knitting is performed using either pointed knitting needles, knitting looms, or knitting machines.
Crocheters don't use pointy needles or machines to make their projects; they use a single crochet hook. The hook can be small or large, or any size in between; it might typically be made of steel, aluminum, bamboo, plastic, wood or bone, but it's definitely a hook.
Crochet is always done by hand, never by machine. A crocheter's movements are so intricate that, thus far, nobody has been able to create a machine that can duplicate them.
At this point I should mention that if you come across something that purports to be a "crochet machine," it isn't really a machine that can crochet. In the course of my career as a textile designer, when I've occasionally encountered these, they've always turn out to be something along the lines of a machine that can do blanket stitch or variations thereof.
So, to recap, crochet is performed using a single crochet hook, and is always done by hand rather than machine.
There are important structural differences between crocheted fabric and knitted fabric.
Before I get any further with this article, I should mention that, thus far, we've been discussing "weft knitting," which is the type of knitting that hand knitters (and some machine knitters) do. There's another category of machine knitting, known as "warp knitting" or "Raschel knitting." Structurally, warp knitted fabrics differ significantly from weft knitted fabrics, and the following points do not accurately describe warp knits.
Both crochet and knitting involve manipulating loops of yarn; with (weft) knitting, the loops build on each other in a way that requires multiple active loops to be held on the needles. Each stitch depends on the support of the stitch below it; if a knitter drops a stitch, the whole column of stitches below it might unravel.
With traditional crochet, there usually aren't many active loops at one time -- usually only one loop, or possibly a few loops. The stitches build on top of each other, but the active loop is the only spot from which the fabric is susceptible to unraveling.
Tunisian crochet is a bit different; this technique combines elements of both knitting and crocheting.
It's impossible to objectively discuss which technique is "better" for any given type of project. I get occasional questions along these lines - "Which is better for making afghans, knitting or crochet?" "Is it better to knit a hat, or crochet it?" I am sure these seem like perfectly reasonable questions, at least to the people who don't know much about either technique. The truth is, the "best" technique for any given project comes down to personal preference. Both of these needle work techniques are worth learning, knowing and using.