In the last two Territory Wars I noticed that my guild is getting points somehow, while I am the only member who participated. And I didn't even kill that many enemies. How did these points get collected and what can my guild do with them?

Here's a screenshot. My guild is Cheerful and I play Diamond server.

You also get points if your guilds name gets on one of the crystals. Points are mostly first gained by the crystals (the higher your name is on the list the more points you get) and then they get higher by kills.

Even though you are the only one, you probably spiked high damage on crystals with op crits or that sort, or the game recognizes no other guild that spiked higher than you did. Seems to me like you did decent damage to 2 crystals with lowest points, 120 pts each, then somehow killed 20 people? lol, maybe your other guildies are playing, as 260 pts for single person is kinda hard,

But what good do these points do?
Is there a ranking or something, because TW isn't of much importance to our guild, at this moment.

Those points determine the winner of that tw, and the winning side gets more tw boxes than the losing side (most of the time, unless people afk and not dps crystals). The guild with the most points wins for their side. Also, if a guild has less than 3 territories, they will add their winning to their total accumulated territories and can get daily gold from the fame turn-in of the area won. The gold you get is determined by your level, and you can only get the salary you win with above lv30 and >200 guild fame.