Correct sentence is May i come in sir/madam? used when you enter in classroom/room/office. you are asking for permission.

Have is used to show possession. example I have two hands. I have one child.

feel surprise.

nothing much. what about you?

Correct Would you like this app?

because in honest 'h' is silent. and after that character 'i' is vowel. hence an is used before honest.

's is used for plural for example boy - boy's car - cars's for denoting multiple things

What is your name? correct you are asking someone about his/her name

Example I was shocked when i heard about your accident or any bad news.

Something that join or connects