OK to ask people how they prefer to be addressed. Older people are addressed by title and last name until they ask you to use the first name. Mrs., Mr. or Miss are used with last name-not first name. Ms. is ok if uncertain whether a woman is single. Use of nicknames is common.
Most parties are very informal chances for people to gather, talk, and relax.
Your host wants you to feel at home. Americans are curious people. They will ask you A LOT of questions. Some of the questions might seem silly, but try to be patient. Gifts are usually given to relatives or close friends.