Resources and materials
There are many, many more resources available to learn maths than are listed here. These are selected, quality, free materials I'm actually using to complete my curriculum. I sometimes choose to make author/institution donations, but I only use materials where that's not necessary.
Where I use textbooks, worksheets, etc., I use only those with a Commons/Open license so that I can attach the whole book to these pages for you, with proper attribution.
I've tried these. They are helpful, high quality and free.
The definition of a textbook gets a little loose here. A well organised set of web pages differs little from a PDF textbook. I'm not going to differentiate too much. I call it a textbook if I can one-click download the whole to my computer, read it offline, and attach it to these pages for you to do the same.
How_To_Study_Math.pdf (Paul's Notes by Prof. Paul Dawkins) Common_Math_Errors.pdf (Paul's Notes by Prof. Paul Dawkins)
I'll try to learn a topic from each of these, and add them above if they prove helpful, high quality and free.
These have courses from several providers. The free courses from quality providers will need finding. Some courses have both free and paid options, the latter giving a certificate or similar.