For these two expressions
Some of my friends will come at 6 in the evening.
Some of my friends will come around at 6 in the evening.
I would like to know if these two expression differ in meaning? Does adding around change the meaning?
The version with come is a bit more formal, and implies that your friends are coming specifically to visit, or at least that the main purpose of their trip is to come to your house (to be at your party, to play poker, to have dinner, to watch the big sporting event, etc.).
The version with come around is more informal, and implies that their visit to you may be only one portion of their outing, and possibly quite brief or minor; they may intend to go see a movie, or eat at a restaurant, or some other thing, after they have stopped to visit you for a while. Indeed, they could be "coming around" simply to pick you up to go with them.
Around adds a degree of informality and approximation to the second that is lacking in the first.