So I'm learning about simple harmonic motion, and I came to the part where the differential equation
$$\frac{\mathrm d^2x}{\mathrm dt^2} = -\frac{k}{m} x$$
is solved and simplified to
$$x(t) = A\cos(\omega t - \phi)$$
So here, I don't get why the angular frequency equals the following value
$$\omega = \sqrt{\frac{k}{m}}$$
I tried to see if this has any evident reasonament to see why this is dimensionaly correct (especially with the square root). I already search for different posts here on Physics where it's explained, but the maths behind them are too complicated for me, and also they didn't answer why this is dimensionally correct.