Displaying ∂u/∂t but only get ∂u() and displaying 2nd order ode

[Anthony The Koala]

Thank you for your time.
Background information
Using the top row button, 3rd from the left one can select a set of templates such as:numerator/denominator a number raised to a power, as well as ∂u/∂t - the u and t are squares you inset in the squares.

Before I have been able to display in the home screen ∂u/∂t

I want to display

∂u/∂t

BUT now only able to display

∂()

How do I display ∂u/∂t?

How do I display ∂²u/∂x²

Thank you
Anthony, Sydney