This is a short list of websites I most commonly refer students to for extra practice. These can be used for free or students can create an account to save their progress.
Practice:
IXL Practice questions in a straightforward format
Khan Academy Videos and examples, along with practice questions and quizzes
Kuta Printable practice worksheets with answer keys (click on "Free Worksheets" then choose your math level)
Resource:
Desmos Online graphing calculator
Wolfram Alpha Explanations and useful widgets (for example, they do a calculator that divides polynomials for you)