Hi,
These questions may seem basic, but i suspect that many people find them awkward to understand because the wires are not actually connected together, the windings are seperate and do not connect together. (normally)
Firstly, the transformer would become overheated if it were trying to deliver more power than it was made for.
Feeding into a short circuit is a case where excess current would be drawn, and cause overheating.
Spot welding transformers do this for short periods, not for 'a while'.
The other question is deeper, and requires an understanding of the way power is exchanged between windings.
Typically where two windings are on a transformer, the number of turns on each winding, forms the relationship between the windings.
Briefly, same number of turns means one-to-one, same out as in.
More turns on the secondary, higher voltage out, and draws more current from the primary.
Less turns on the secondary, lowers voltage out, and draws less current from the primary.
The windings have no electrical connection, the power is transferred by the magnetism (flux) operating within and around the windings, guided by the ferrous material.
Lower frequencies need more laminations or ferrous material,
Higher frequencies need less laminations or ferrous material.
Much higher frequencies often need very little or none.
The current draw in the primary is in proportion to its turns ratio with the secondary.
In this case, 220V primary - 12V secondary, the proportion is roughly eighteen to one, so the primary current draw would be one eighteenth of the current drawn by the secondary.
So a 12 volt lamp drawing about an ampere, would take approx 65 milliamperes from the primary winding.
The above is only a brief overview, and may not apply in all cases.
For a fuller understanding there are many in depth studies available on the net.
This is only to illustrate the mechanism between windings.
Regards, John