@SweetHao1996,
Where do you start a conversation with a stranger?
You just donĀ“t walk up to someone and ask questions.
So where?
In a public tranportation.There you can ask about the sights in the city even if you know them, or in a train about the places you pass, if you are allowed to borrow the newspaper.
In a cafe ask at the next table what they would recommend
At H&M ask a girl of your age to help you pick out one of the outfits you are trying on.
Supermarket - look confused and ask a senior citizen about the local cooking and if she could please help you come up with some ideas.