Formulae for energy of photon (E=hf and E=hv)
I understand your confusion. They all are actually the same formulas. It is because lets start with the first equation,

$$E=h \cdot f$$

But we know that frequency can be written in terms of speed formula,
$$ v = f \cdot \lambda$$

Which can be rearranged into the following,
$$ \frac{v}{\lambda} = f $$

If you put that expression into the above equation, then that becomes

$$ E = f \cdot \frac{v}{\lambda}$$

Hence the same formula can be written in many ways. 



Your first two equations are just the same. $f$ usually stands for frequency and in the second equation you have just used $\nu$ for it. That is the frequency of the photon that is coming in or being released.

Whereas your third equation actually comes from the speed formula as I have written above,
$$ v = f \cdot \lambda$$

Rearranging for frequency, you get:
$$ \frac{v}{\lambda} = f $$