I do a game for the school

Hello. I am new to Unity. I'm still in school. And we must learn unity alone I'm not very good at English, but I'll try to explain

We received a draft in late March: develop a game I did all the modeling in Maya (3D software) that passes easily in Unity, I put the collider, I put the character, lights It's all ok

But what complicates the code, I don't know where to start I'll make a list of everything I need to have

I have a mansion, with 4 rooms (hall, living room, attic and a bedroom)

In the hall, I have a system of junk, I must pick up 5 items and I win the key area and a puzzle piece that will serve me in the attic and I win also a key , the key of living room I go to living room : key -> open the door Here a new junk, I collect objects and I win a mini key and the bedroom key

I return to the hall, I go to the back of the hall, where is the chest (coffre), I use the mini key won (key -> chest open): I won a blue crystal and the key of attic

I returned to the living room, where another chest, but with an automatic code, so I think the code , I win a green crystal

I go to the attic : I use the won key. Once inside, I see a puzzle on th floor, with a missing piece : I inserts the piece win in the hall in the junk I win a red crystal

Then I go to Bedroom, I use the bedroom key , once inside, a A small screen appears: get the orange crystal Once you find, I go in the hall, I me put large front door, I click on it, - if I have the 4 crystals I am free, - if I haven't the 4 crystals the door remains closed

I guess for all that, it will be hard I do not know where to start But since I have several times the same thing, I probably will use the same code

Sorry for the translation, it is google translation

Thank you !!