All you really need to begin knitting is a set of needles and some yarn.
Needles can be made of many types of material, the most popular being metal, plastic, or wood / bamboo. Metal needles will be slippery compared to wood, so I suggest using wood for more control - stitches won't slide off the end of the needle as easily when you don't want them to!
Yarn comes in all sizes from very thin "lace" weight to super bulky. I love the feel of the bulky "Rasta" yarn from Malabrigo. I've made one hat and scarf set, and am making another scarf. It may be a little too thick for beginners, but don't start off with a really thin yarn.
A "normal" yarn would be anything called "worsted weight", and that type of yarn is perfect to start with. For knitting a scarf with worsted weight yarn, choose a needle size 6, 7 or 8. Gauge is not important in a scarf, but often you will be told to "check your gauge" for other projects. More on that at another time. A long scarf will take about 3 skeins of yarn. A hat will use 1 skein or less.
Find a free pattern to follow, whether a scarf or something else, which will tell you needle size, yarn type. I have a section of free patterns saved on my Pinterest knitting board.
Choose a light color yarn because the stitches are easier to see. Merino wool comes as machine washable or hand wash. Unless you want to hand-wash your item, look for yarn that can easily be cleaned. If you wash a wool item incorrectly, it can shrink up and "felt". You don't want that to happen after all that hard work!