I just have created a new proposal in Area 51.
Now I need to create tags, that I have in mind, but I can not find where could I create them.
How can I create tags for my proposal?
Area 51 proposals simply have no tags. It's not part of the system. You only define what the site should be about, and let people post example questions.
As Jeff explains here:
I worry that creating pre-defined tags so early would affect the example questions people submit, though -- and the example on and off topic questions are by far the best way to figure out what a site "is".
And Robert also says here:
Area 51 is not a "subject of expertise" and this is not set up like a generalized Q&A site. That's the basics of it.