Often you want to find a function that is a solution to a given differential equation which at the same time either passes through a specific point, or has a specific value, for a given $x$-value. This extra requirement is called an initial condition. It enables you to determine the constant of the solution.

When the constant is determined, it is called a particular solution. You find the particular solution by inserting the values of the initial conditions, and of $x$ in the function, into the equation.