Tips on repairing Shimano brakes on my Bianchi cortina?

[iluvmybike]

Looking closely at that photo it looks to me like the silver arm (cable hook unit) on the brake where the cable fits has been opened up and the ends distorted - not uncommon if the handlebars get spun round the wrong way and it yanks it through (often seen on kids bikes). It needs a new set of brake arms. They are not hugely expensive

 

[Cycleops]

Looking closely at that photo it looks to me like the silver arm (cable hook unit) on the brake where the cable fits has been opened up and the ends distorted - not uncommon if the handlebars get spun round the wrong way and it yanks it through (often seen on kids bikes). It needs a new set of brake arms. They are not hugely expensive

....but might be a little daunting for a newbie to bike mechanics. Easily

bent back into shape with a narrow nose plier.

 

[Mr Celine]

View attachment 543766

The end cap of the “metal cable guide“ (called a noodle} has become detached from the “cable hook unit”. As above squeeze the arms together to reattach, if that’s difficult undo the cable clamp bolt to release the cable and try again While pulling the cable end.

Nice clear diagram but you shouldn't need to slacken the cable clamp bolt. If the end cap was dislodged accidentally it would suggest that the cable is if anything already too loose.
OP when trying to re-fit the end cap into the hook unit ensure that the ends of the outer parts of the cable are fitting snuggly. In your photo above the black brake cable outer has to be pushed fully into into the end of the noodle (metal cable guide).
If the cable is too tight or your hand isn't strong enough to hold the arms (brake arches) together you should be able to slacken the cable at the adjuster, which is where the cable exits the brake lever. It may have a locknut which has to be slackened first.

Remember to check your brakes are working once everything is reassembled. If necessary adjust the cable tension with the adjuster at the lever.