Get current user Info :

Lightning Controller : var currentUserId = $A.get("$SObjectType.CurrentUser.Id");

Apex : User userObj = [SELECT Id, Name, UserName FROM User WHERE Id =:userInfo.getUserId()];

Assign Tasks to different members in a Queue using RoundRobin technique

Integer IntrandomNumber = Integer.valueof((Math.random() * 1000));
for{
 Group grp = [SELECT Id, Name, Type, (SELECT Id, UserOrGroupId,   GroupId FROM GroupMembers) FROM Group WHERE DeveloperName ='<Name_of_queue>' AND Type =: 'Queue' LIMIT 1];

  if(grp != null && grp.GroupMembers != null &&       !grp.GroupMembers.isEmpty()){
  Integer userIndex = Math.mod(IntrandomNumber,       grp.GroupMembers.Size());
  task.OwnerId = grp.GroupMembers.get(userIndex).UserOrGroupId;
}
IntrandomNumber = IntrandomNumber+1;

}