Algebra is a major part of Mathematics, in that, it is used to find unknowns and accurate numbers to variables. It is especially important in everyday life as it can help anyone with buying/selling decisions as well as help solve many technological problems.
There is a fair amount of draft textbook material regarding Algebra I at Wikibooks. b:Special:Search?search=algebra+I&fulltext=Search
Also more advanced or generic algebra topics. b:Special:Search?search=algebra&fulltext=Search
Information on the history etc. of Algebra can be found at Wikipedia.w:algebra
There is also Intermediate Algebra or Algebra II from Wikibooks.b:Intermediate_Algebra