Okay – some advice I got after a similar thing last week
First up – I made an improvised cage from an upturned recycling crate placed over some cardboard and newspaper.
Next: Don’t let it get stressed – bird have only got little hearts and you chasing it round the house will freak it out. If it is squawking and stressed then cover the cage with a blanket till it calms down.
You can try placing the cage outside for a while: if its parents are still around then they may be drawn to its crying and you an reunite them (this is really its best hope).
Otherwise you’ll be needing to feed it. We got a tin of high-protein cat/dog food from the vet. It was basically a paste and we fed ours by gently holding it and presented a syringe like a mother bird trying to feed it.
Be aware that baby birds need a LOT of food. If it can’t feed itself then you’ll be needing to feed it every hour or so during daylight.
Don’t forget a little water as well!