Fig. (?) A reference to a picture, by the Anno Fabri tag it was uploaded under, wherever that picture is:
Up to four tags, with the plural and the and written for you, exactly as {{eq}} does for equations—and for the same reason: this is that template's twin, built on Module:Fig as that one is built on Module:Eq. The word and the first tag are held together by a white-space:nowrap span; the commas and the and of a multiple reference are ordinary places to break a line.
The tag is the picture's own name. Every image the composer uploads is called lw-tag.png after the second it arrived (MediaWiki:Gadget-microblog.js), so a figure of any 𝕐 or ℤ post can be referred to at once, with nothing to write into the page first. A picture that came in under some other name is given a tag the first time it is Ctrl-clicked (MediaWiki:Gadget-fig.js), which is also how a picture is given an exact landing place and a Fig. (tag) caption to say its name on hover.
Which page. With no in= the tag says it: it is an instant, and the month page of that instant is tried, 𝕐 then ℤ, then the month before it—a picture uploaded at five to midnight can be posted after midnight. The page holding the reference is asked first of all, a post crossposted to ℤ carrying its pictures with it. Say it outright with {{fig|07tuF|in=September (2026)}} for a picture anywhere else, and then that page is the only one looked at.
Where it lands. On the picture itself where the gadget has left an anchor, on the post holding it otherwise—the same landing an equation reference gets, worked out by the same function (Module:Eq's _anchorAt). A tag no page can account for prints in red-dotted underline rather than quietly linking nowhere.
Not to be confused with {{figlabel}} and {{figref}}, which number the figures of one page in order of appearance and refer to them by that number: that is the right tool for an article that says Figure 3, this one for pointing at a picture across the wiki by the name it has always had.