I don't think you need Foundations, no - that's only the lower-level stuff and you appear to be fine there. You can start with the regular books.
sometimes in algebra I use substitute to find the answer instead of try to solve the equation
That's fine - that's not a problem. This is not a school test - HOW you get to the answer doesn't matter. They don't look at your work. You want to use whatever method you think is easiest / most efficient.
You have a basic choice to make: would you like to work on your own or would you like to join a class (or work with a tutor)?
If you study on your own, here's how to set up your study plan and get going:http://www.manhattangmat.com/blog/index ... ould-i-do/
If you decide to take a class, follow the syllabus that comes with the class.
Feel free to come back here with any questions! :)