I've just tried running the latest installer
I simply double click the exe and it opens a window where I can select language
Then a few splash screens followed by a welcome screen, I clicked "Continue"
Then I had to accept the end user licence, I did
Then I had a screen with installation options with it defaulting to C:/Program Files (X86) / Zenimax Online
and giving you the option to change, It tells you how much free space there is on the drive it's set to install to, as others have said you need 60GB for it to install (although once installed it takes up just over 30)
Make sure you have enough free space, if not, change to use another disk drive (presuming you have one)
I quit at that point as I already have the game installed but from memo you click install and it goes away and does it's stuff.
In beta at one point, for some reason I had to free up around 80GB before it would install, when I had 60GB it still refused to. But again once installed it took up about 30 GB