If you are new to the world of radio, you may not yet have acquired much information about antennas.
There are a few general principles to abide by when it comes to antennas. This video explains the basics, and also includes a demonstration proving that bigger is not always better.
This is basically a primer designed to help you get the most out of your SDR, or your SDR bundle (see below).
If you purchased an RTL-SDR v3 bundle or a NooElec bundle, they each come with antennas you can use to start receiving right away. However you will want to adjust them for best reception. The video gives some basic theory so you will know how to do this best.
There are also some important tips to follow that will enable you to receive more signals.