1- To make tea you need to boil some water

The first one is probably the more correct and natural if it is just an explanation. Maechy's description of the different meanings is perfect, and so if the second one was intended as giving advice or instruction, it would probably be more naturally worded as "You should boil some water and make some tea."

Using "should" denotes advice while "need to" a necessity. You need to drink some water. (You're too thirsty, you might collapse if you don't drink some.) You should drink some water. (It's an advice from me to you. Probably you just finished having your exercise so it's best you drink some water.)