You have several different queues that you'll need to keep track of. The first and most obvious one is your building queue. You can have up to two buildings being worked on at a time, whether they're being built for the first time or getting upgraded. The second queue is your research queue. Research grants you passive bonuses to a variety of aspects about your base, so you should research as much as you can. You can have one research in progress at a time. The third queue is your Barracks. The barracks is where your troops are stored and trained. The more troops you have on your ships, the better your chances. You'll want to have as many troops as you can on hand, as they take quite a time to train.