hi, elizabetta!
i just posted some information on this on another forum. so, forgive me for doing this, but i am just copying and pasting what i posted. i recommend the math.com site for basic math review. happy studying!
http://www.math.com/homeworkhelp/basicmath.html - this will take you into a review of basic math. if you want to progress to more difficult math subjects, click on the "select subject" drop down box on the upper left margin. this site is a nice, simple review of math concepts and will take you through step-by-step explanations as well as a few practice problems.
http://www.purplemath.com/modules/index.htm - this is without a doubt the best site for information about algebra (basic and intermediate, both) that i have seen. this is a page of links to subjects in algebra. there are step-by-step explanations of things, some are several pages long.
http://medi-smart.com/student-math.htm - math for morons. i found this site recently and haven't had a chance to explore it enough. however, there are links to other math sites to check out as well as some basic information on math, starting with pre-algebra (which is basically 8th grade level math). you start on the left margin by clicking on an area of math (pre-algebra, algebra, geometry, algebra ii or pre-calculus/calculus). that brings up another page of links of various math subjects covered in those areas. clicking on one of those links brings up an explanation with a couple of example problems and ends with a quiz you can take. at the end of the quiz you will be told which problems you missed and what the correct answer was and why. i had problems with the quiz since the questions appeared in a pop-up window that cut off some of the text of the questions.