Where to learn Drupal from scratch?

I have to learn from scratch within a week.

It took me a year of working with Drupal every day to get even slightly comfortable with it, and I was already a comfortable PHP developer. I wish you luck in a week, but realistically, it's not going to happen.

That said, starting with a course on Drupal is your best bet. https://drupalize.me/ has a good set of Drupal tutorials. If I were in your position, it is where I would begin. Good luck!

Tell whoever gave you that requirement to go pound salt. 

Just learning to administer a Drupal site, without ANY programming, takes months if not years ... even if you are an experienced web site admin with other products. 

I'd start by asking the requirements givers how and why they determined that the site should (must) be in Drupal. 

I have to learn from scratch within a week

One of my clients has hired a young man who is required as part of his job to learn Drupal. They have arranged for him to to attend a Drupal apprenticeship for 18 months. I have taken a look at the apprenticeship, and the quality of the syllabus and of the people involved seems very good. You might want to suggest that to your employer. They do not expect him to know enough to replace me after 18 months. However, he will have all the skills to do all the basic tasks you are likely to encounter on Drupal 7 and Drupal 8.

https://groups.drupal.org/node/492233, probably more than a weeks worth.

Hope for you that the other requirements are such that they can be easily implemented. Preferably with core drupal or only a few extensions. 

There seems to be some confusion about what was meant with:

I have to learn from scratch within a week.

Assume that you need to start working on the project in a weeks time. In which case you'll be learning on the job, like anybody else.
Are you allowed/willing to share details of the project here?