Queues are all rating based and your rating will be adjusted in all of them. Here are the different types of games you can have.
A Private game can be made through a party of 8. You create a party, invite 7 of your friends and as soon as everyone is ready the game will start.
The Ranked queue is for people who want a ranked pugging experience with parties of up to 3.
The Scrim queue is for parties of 4.