Algebra has many applications in many areas of maths and science, but also quite often you will use algebra in real life without you even knowing that you are doing it. When using a recipe and you are halfing/doubling the ingredients, or calculating the price of a product that is on sale ... You are doing Algebra!
Algebra involves doing computations with non-numerical mathematical objects, an example of an algebraic equation is $y = 2x$. Where you can substitute $x$ for a numeric value and calculate a value for $y$. We can use these non-numerical symbols to represent either unknown or unspecified numbers. In physics algebraic equations are used to represent the scientific relationship between certain variables, the most famous being Einstein's $E=mc^2$,