You can download Houseparty on your phone from Google Play on an Android device or the App Store on your iPhone. Once you have downloaded it, you will need to create an account with your email address, phone number, and username.
When you're done, the app can automatically connect you to people you know with your phone's contacts directory. Just click Add to send an invitation to a friend. By installing the Houseparty desktop software for Mac or Windows, you can also use Houseparty on your phone.