Hi CosiestGalaxy23!
To run the game, just do the following:
1. Find where the file was downloaded (It's name is something like "NovaIslands-PreAlpha-4-Update-1.01.zip")
2. Right-click the file and search for "Extract here"
3. Look for the folder "NovaIslands" and double click it
4. Inside the NovaIslands folder, double click the file "Nova Islands.exe"
It's important to notice it's only compatible with Windows right now.
And if you have any issue, just let us know :)