What are your full computer specs?
Has it worked OK with the same footage and effects previously?
Nobody can tell you anything without exact system info or other technical details like your preview settings, comp settings and so on. Just saying that it is slow is useless.
The first clue to an answer for you comes here:
I'm new at this, so I'm looking forward to any advice.
Welcome to the world of visual effects and compositing. You need to render previews before they playback smoothly. The more complex the composition the longer it takes to playback. AE is not a Non Linear Editor and it doesn't behave like one. AE is specifically designed to do things to shots that you cannot do in a NLE. Most AE comps are one shot that has been trimmed to the length used in the final edit. You should only spend time working on frames that you are actually going to use in your final composition.
AE's UI is complicated with literally hundreds of thousands of possible combinations of settings and switches. Visual effects workflows can be extremely complicated. Spend some time learning about the proper workflows using trainers you have properly vetted. YouTube is littered with thousands of tutorials by amateurs that promote poor workflows and poor work habits. The Search Help field at the top right corner of AE should be one of your best friends. If you have any budget at all get some professional on line training in AE from folks like Total Training or Lynda.com. Use tutorials from 3rd party plug-in and script developers like Red Giant and Imagineer Systems before you start looking at YouTube or Google when you are trying to use their products. Spend some time here to get started: Basic AE
Are you still facing this problem? If not, let us know how you solved it. If so, please let us know so we can assist you further.