not a stupid question per se - but it works like that:
You build Tier 1 Installations and get Tier 2 points for that. Depending on what you want to build (and when) you need two or five Tier 2 points to be able to build a Tier 2 Installation.
Same applies for Tier 3 - if you build a Tier 2 you get 1 (or 2?) Tier 3 points, and for a Tier 3 facility you need 6 or 12 points to be able to start the construction
This is generally the case, except that Settlements seems to be bugged. You can build a medium Settlement and get a T2 point, but it seems they end up as a small once complete. You can use that T2 point to build a large Settlement, and get T3 points, but they end up as a medium once complete. So you get the right Tier points, but the Settlements are one size smaller than the one you placed and contributed materials for.
At least this is the case for all of my 8 Settlements that I've placed. I didn't realise until someone said they couldn't land at one, and I found it had a small pad, even though it was a medium that I built. And before anyone suggests it, no, I didn't make any mistakes, because I've been recording all that I build, including the size and mats used (research for a website currently under construction), and they all match the medium and large that I selected, yet they ended up one size smaller once complete.