@LeakyNun It is like this. Consider the initial value problem
$$y'' + p(t)y'+ q(t)y = g(t), y(t_0) = y_0, y'(t_0)=y_0'$$
where $p, q$, and $g$ are continuous on an open interval $I$ that contains the point $t0$.
Then there is exactly one solution $y = \phi(t)$ of this problem, and the solution exists throughout the interval $I$