Voldemort's physical presence pre-Goblet of Fire

Question

Voldemort returned to physical, human form in the Goblet of Fire. But can someone explain what the physical effects of using the curse on Harry as a baby had on his body? He didn't die but also, wasn't human. What was his state?

Also, when Wormtail put him into the cauldron in HP4, he was nothing more than a small baby-like creature. Where had he been before he was under Wormtail's care? He didn't look capable of taking care of himself or even moving. Was it ever explained where Wormtail actually found him?

Answer 1

This explanation is given in Harry potter wikia:

After his escape from capture at Hogwarts, Peter Pettigrew(Wormtail) had no choice but to rejoin his master, or Sirius and Remus would surely kill him. He went to retrieve Voldemort's wand, then travelled to Albania where he learned from the rats there of a place in the forest where the creatures feared to travel. They said a dark shadow (Voldemort) took over the animals and killed them.

On his way to his master, Peter ran into Bertha Jorkins, a Ministry witch who was on holiday in Albania, while she had stopped at an inn for food. Although she recognised him, Pettigrew was able to lure her into the forest and overpower her, before handing her over to the Dark Lord. Under torture, Jorkins gave them information that helped Voldemort make plans for an attack on Harry Potter, including information on the Triwizard Tournament and the location of a faithful Death Eater. Voldemort's rudimentary body.

Pettigrew milked venom from Voldemort's snake, Nagini, to strengthen him and provide him with a rudimentary body. He carried Voldemort's weak, small body on the long journey back to Britain, where they took up temporary residence in the Riddle House outside of Little Hangleton. Voldemort called Peter by his Marauder name, "Wormtail." Over time, Pettigrew tried unsuccessfully to convince Voldemort to use a wizard other than Harry Potter to rebuild his body, but Voldemort saw this as an attempt at desertion and claimed that Pettigrew was regretting ever returning to him in the first place.

There is no explanation of this in movies themselves, but it is explained in the books.

Answer 2

Less Than Dead

It is difficult to answer what exactly he was after he was blasted by his own Avada Kedavra, no-one seems to know, for sure. This is Voldemort's explanation to his Death Eaters:

“I miscalculated, my friends, I admit it. My curse was deflected by the woman’s foolish sacrifice, and it rebounded upon myself. Aaah... pain beyond pain, my friends; nothing could have prepared me for it. I was ripped from my body, I was less than spirit, less than the meanest ghost... but still, I was alive. What I was, even I do not know... I, who have gone further than anybody along the path that leads to immortality.

^{-Harry Potter and the Goblet of Fire, Chapter Thirty-Three (The Death Eaters).
[Emphasis mine]}

Rudimentary Body

Voldemort gains a "rudimentary body" - the childlike weird thing that Wormtail carries around - at the beginning of The Goblet of Fire; using a spell of his own invention coupled with a concoction of Unicorn Blood and Nagini's Venom.

This is discussed further on our Science Fiction and Fantasy Stack Exchange, in how did Voldemort get his body back?