I want to learn math from zero I finished high school 2 years ago and now I'm stuck in a university in Turkey. I am interested in learning precalculus, discrete mathematics, physics and chemistry.
Question: I need to learn math and physics from the bottom, and I mean by from the bottom all the basic material, possibly starting in from precaluclus and up to calculus, etc. I would also like advice for anything related to buying books or searching online for material. Anything would really be appreciated.
Thanks in advance.
 A: As Thomas Andrews mentioned in the comments, Khan Academy could be a good place to start, especially if you have to back really far.
If you've done that and feel you actually remember more than you thought (or when you move far enough along), MIT actually offers a lot of online video/audio lectures and some textbooks for free.  But this would probably be a little ways away.
Also, you can have some practice at websites like analyzemath to test your knowledge (you may remember more that you thought!).
These all appear to be free by the way (although sign-up may be required).
Best of luck to you.
A: You might want to consider the website of public-domain mathematics instructional materials that I have created.
The materials range in difficulty from kindergarten to college, but the bulk of them are at the high school level.
The address is www.public-domain-materials.com.
These materials, under development for over 30 years, have been recognized by a congratulatory letter from the U.S. National Science Foundation.
The website also contains a large amount of language-arts materials.
The materials are almost all in English. (A few are in Esperanto.)
The materials are all downloadable (or freely available for reading and copying). There is also a section of interactive exercises. Here is the link to the algebra exercises, which can also serve as a portal to the website:
http://www.public-domain-materials.com/online-algebra-exercises-and-answers.html
The website contains a link to the NSF congratulatory letter.
Regarding finding useful videos on any topic, you might want to consider Mashpedia, at:
http://www.mashpedia.com/
A: Since making the post below, I have found an even better way to learn math starting with simple algebra through precalculus--the precalculus class sponsored by Arizona State University on edx.org at https://courses.edx.org/courses/course-v1:ASUx+MAT170x+2T2017/course/ featuring the Aleks tutoring software.  Aleks, like schoolyourself.org, tests your skills and keeps track of those you have learned, but it is has more material and is more comprehensive.  The course is free unless you want a certificate.

If you really want to start with a lot of elementary stuff, like addition and subtraction, I suggest you look at 
https://schoolyourself.org/
which I started using yesterday.  
I wanted to review math from the ground up myself.  I completed in-person classes through Algebra II and Trigonometry many years ago but have forgotten a lot and have been having difficulty getting a good start on calculus as a result.
The site at schoolyourself.org is interactive and adaptive.  I was able to zip through most of the early units on basic arithmetic in several hours. The site lets you turn the sound up to double speed.  If it detects that you know the material there is very little repetition, but it offers help and gives you additional explanations, practice, and review where it detects you are having difficulty.  The topics listed go all the way through calculus and statistics, though I have not gotten that far yet. 
Even in the early material I found things to ponder, like the significance of the fact that division by zero is undefined and of the apparent asymmetry between the way positive and negative numbers work, and why computational tricks I learned years ago, like cross-multiplication to compare fractions with different denominators, actually work.
The site was apparently bought out a couple of years ago, and does not seem to have developed since then, but what I have seen there so far is the best of its kind I have been able to find.
