@outlander and anyone else who is interested too. 
@CheerBear is doing awesomely as usual explaining for you Outlander. I'll add a couple of things because I can knit too as well as crochet being my favourite craft skill, so might be able to help there.
Put really simply,
Knitting = 2 sticks (needles, and sometimes called knitting pins too - different countries, differnent names sometimes)
Crochet = 1 stick (hook - but sometimes uses a knitting needle with a crochet hook to make special laces like broomstick crochet which you might come across in some of the Outlander series stuff)
Knitting requires you to hold a needle in each hand and to form the stitches with yarn on one needle at at time, while crochet is formed by making loops of varying lengths with the hook and yarn.
Yarn is the generalised term for the string used for,w ell, yarn work, it used to be called Wool, because wool was the only yarn availble, now there are so many and varied yarns available that it is more accurate and really better to call what is being used as Yarn.
Yes, it is possible to use practically anything that can be turned into a yarn/ string for knitting or crochet. Plastic or PLARN is really hard to use, and you have to make sure you're not using quickly decomposing plastic bags or the end result isn't work the time and effort.
Many clubs make blankets for the homeless from Plarn. It's a worthy and interesting project.
There are some explanatory images a few pages further back about tatting Outlander - but it's way back now so here are some images and an explanation.
Tatting I do is done with a shuttle that has thread (tiny a bit like sewing thread only better quality) wound onto it either on a bobbin or on the post of the shuttle (I use bobbin shuttles). A knot is done by manipluating the thread with the shuttle, there are only 2 knots to tatting, a bit like one of the macrame knots. these knots on the threads are worked into patterns that form delicate lace for all sorts of things like edgings on hankies, whole table cloths and garment embellishements. This is a board with lots of tatting examples pinned for demonstration. and then there's a hankie I had been working on. The pink is no more cos I cut of one of the picots by accident, so now it's just the white edge on it's own, which is still pretty. Feel welcome to ask any questions you like if I have not answered well enough. 
