--> Mr. Cunningham,  this is the only person Scout had recognized
--> The mob was group of men(they weren't specific with names) they were presumably from Maycomb. They weren't that polite to Atticus.
Quote:  "It was a summer’s night, but the men were dressed, most of them, in overalls and denim shirts buttoned up to the collars. I thought they must be cold-natured, as their sleeves were unrolled and buttoned at the cuffs. Some wore hats pulled firmly down over their ears. They were sullen-looking, sleepy-eyed men who seemed unused to late hours. I sought once more for a familiar fare. and at the center of the semi-circle I found one. “Hey, Mr. Cunningham”"(Lee 204).

Purpose of Mob: The Purpose of the Mob was to disturb Tom Robinson in Jail. Although what they were going to do was unknown Atticus had went to the jail to stop them from bothering Tom Robinson or fight with him. They had left because the children were there.
Quote:  "Atticus stepped back and looked up. "They've gone," he said. "Get some sleep, Tom. They won't bother you any more""(Lee 206).
How they got there:  They arrived in 4 cars and drove to Maycomb jail just like Atticus did. They had left using the same cars because Atticus and the kids stopped them.