You see reply... and next to it reply with quote... and next to that a little box. That little box is 'multiquote'. Hit multiquote for each post you want and then on the Last post you want added hit the 'reply with quote' (Not the multiquote) and it will quote everything with multiquote and also the last one you did as reply with quote.
You can then respond inside each quote. So at the end of one quote, you can type a response, and the same for each quote after. Though if you do this make sure to pick a color that will stick out. Since most people type in black, red is usually good.
Keep in mind you still have to put 10 spaces outside of the quotes, in the normal typing box, or it wont send it.
Also, a good tip, is if you hit 'go advanced' before posting, it shows you how the post will look before posting it. This works well when you add pics, vids or links, to make sure they work, are displaying, and that you have the right one haha.