If you point to something, you point with one finger but if you want to be more subtle, you can just stretch your head, or move your eyes in the direction you want to point.

When you beckon someone you move you whole hand toward yourself. in a downward motion. 

When you wave goodbye, you move your hand from left to right, or, you close your hand and open it, so that the outside part of the hand is toward you.

Holding the door for the person following you, or even helping a person with overweight baggage is a sign of politeness, but it is not expected.

In traffic, when you give someone right of way, it is polite to say thank you by nodding the head, or showing one hand.

At school, when you want to answer, you raise your  hand, and hold two fingers, just like the “ peace “ sign.

For approving something, or saying "ok",  you just raise your thumb.

If you`re going to a store, always say hello and bye to the vendor, and thanks after you buy something.