What is difference between Queues and Public Group and when do we use public group or Queues in Salesforce?

Queue and groups are both are same ,which will hold group of users, But in working environment we can functionality we need to decide which will use in proper way,

Suppose in the case of Lead Assignment,

1 . Scenario like Each user should assigned to at least one lead and same number of leads.

That means user need to handle assigned lead individually and all users in organization should assigned with same number of leads, in this case we can define users in organization as Queue and assign them one by one and in same number using round robin lead assignment.In this case we can achieve above scenario.

2 . Suppose you need to Share some of the information in your organization among some users, in this we can define Group ,then we can share information or we assign some work to group.Here this is Group effort.