Most probably you will not get it immediately (especially if you don't have a high-end Samsung device), but these are steps for joining a waiting list.
- Follow this link to the official Fortnite beta website
- Sign up with your email
- Wait for the invitation email
- Open the link from the email and download "Fortnite Installer" app
- Install the app ("untrusted sources" flag in system settings should be enabled)
- Open the app and follow further installation instructions
Don't forget to like Fortnite beta page on TestingCatalog
Fortnite for Android is a long-awaited game for many people. Apparently, it will not be available on Google Play in nearly future. Epic Games made a decision to distribute Fortnite *.APK through their own website directly.
Apart from that, Fortnite Beta is only available for Samsung devices exclusively for the first 3 days after the Galaxy Note 9 announcement. After that, it will become available for all other Android devices which are capable to handle Fortnite requirements.
Here you can find a list of all capable devices:
- Samsung Galaxy: S7 / S7 Edge, S8 / S8+, S9 / S9+, Note 8, Note 9, Tab S3, Tab S4
- Google: Pixel / Pixel XL, Pixel 2 / Pixel 2 XL,
- Asus: ROG Phone, Zenfone 4 Pro, 5Z, V Essential: PH-1
- Huawei: Honor 10, Honor Play, Mate 10 / Pro, Mate RS, Nova 3, P20 / Pro, V10
- LG: G5, G6, G7 ThinQ, V20, V30 / V30+
- Nokia: 8
- OnePlus: 5 / 5T, 6
- Razer: Phone
- Xiaomi: Blackshark, Mi 5 / 5S / 5S Plus, 6 / 6 Plus, Mi 8 / 8 Explorer / 8SE, Mi Mix, Mi Mix 2, Mi Mix 2S, Mi Note 2
- ZTE: Axon 7 / 7s, Axon M, Nubia / Z17 / Z17s, Nubia Z11
If your Android device is not on the list, you will have to wait until it will become officially supported. I don't believe that anything below Android 7 will ever be supported but nobody knows that for sure.