Can anyone help me with a few questions about Korean culture for a class? It'll take 5 minutes!

Yes and no are pretty standard. A gesture for yes would be a nod. 'No' can also be the standard shake of the head but I have also observed Koreans do a wave of their hand, like you're swatting at a fly, to accommodate saying no. Koreans also do a thing when they speak that also applies a bit to gestures in which they emphasize a word/gesture to also emphasize the meaning. For example, an exaggerated nod for yes might be used in a situation where you two are agreeing on something...say a point in a debate.

Greeting someone can be very complicated depending on your relationship with that person. Koreans bow, but the degree at which you bow matters. The polite way to bow is to cross your hands over your diaphragm and bow at around a 60 degree angle. The degree at which you bow is important. A 90 degree bow is most respectful but not entirely practical, but a slight bow could be seen as disrespectful. A variant, and more standard way to bow, would be to place your hands at your sides, but its weirder for girls to do this.

Of course, the highest form of respect is to kowtow (essentially getting down on the ground to bow) to someone, usually an elder. But kowtows are done often ceremoniously and would be out of place in a lot of situations. Guys and girls also kowtow differently. Don't worry about kowtowing though as you most likely wont use. Also, Koreans NEVER look each other in the eyes when bowing. (Lot of people mess this up because of Enter the Dragon)

Greeting when you are close to someone is pretty much the same as in the West. You don't have to bow to these people. Also, Koreans shake hands (especially in business situations) but Koreans use two hands when shaking with one hand supporting the other. The rules for this are similar to bowing in that you use two hands to show respect to someone. For example, you don't have to bow at a high degree, or use two hands to someone who is younger than you. Not because you don't respect them, but because the younger people are the ones obligated to show the respect.

The beckoning gesture in Korean culture is different. Imagine if you were trying to fan yourself with your hand. Now just extend your arm with palm facing down, and wave of your hand at the wrist.

Koreans use the middle finger now because of American influence. Although some still use their middle finger to point at something (generally older folk like my dad).

Hope this helps.

greet and beckon are two different questions, so 5 total. Sorry formatting