When you've downloaded the game you need to unzip the contents to wherever you want to save it to. Then you have to enter the folder where you put it, Right-Click and go down to Properties and change it's permission value to execute. Or from Terminal you can just run;
chmod +x V1.04_Raft_LinuxUniversal
you will have two different binary files, you have LinuxUniversal.x86 and LinuxUniversal.x86_64, run it on whatever your system uses.
one you've done this just double click and the game will load.