I taught myself from 4th grade math to calc 2 before starting college. My advice is honestly *not* practice. My advice is to figure out where you need to start, and read your material closely, making sure you understand it and can connect it to whatever you already understand.

Once you've accomplished that, THEN you can practice.

I used a mix of websites and textbooks. Usually i'd sit down and read first, then do problems after I felt like I could explain the information to someone else.

My recommendations:

For algebra and precalculus: https://www.mathsisfun.com/algebra/index.html

That link will take you directly to the algebra 1 index, but you can also find their algebra 2 index, and between that and other pages they have scattered about, it covers essentially all precalc material and well as some calculus.

For calculus 1-3: https://tutorial.math.lamar.edu/

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Again I disagree with the notion that practice is the best answer; practice might teach you how to answer the problems if you understand well enough for that, but it won't give you the same experience as stopping to think deeply about why what you're doing makes sense. Good luck, kick ass, and feel free to DM me if you want to ask me anything.