Where can I find what's the clan tag and otherwise?

u must be invited to a clan first

No! The information. As I'm not participating, but just know which clan has which tag and so on.

you know, to prevent guys talking about clans (using tags) and I get noobd and such situations

Go to the top of the page and click on the "clans" tab, then click list clans.

It will have every official clan with their Clan tag next to it.

Try this.