Easy Filter with FFT and Convolution I'am pretty new to this topic so i dont have much experience with DSP.
I want to filter(highpass) a WAVE file, i have already programmed the FFT, and now want to filter the FFT vector via convolution (which is a multiplication in frequency domain ?!).

1) Can anyone give me an easy equation for such a filter?

2) If i have an equation i compute it, also Fourier-Transform it, an multiply it with my FFT vector and inverse Transform it an i have applied the filter?!
Actually, yes. As Hilmar pointed out, it might be cheaper to use an ordinary filter, but that depends on the circumstances.

If you have two signals $A$ and $B$ with Fourier transform being $\mathcal{F}$, their convolution $A\ast B$ will be 

\begin{equation}
A\ast B = \tilde{\mathcal{F}}(\mathcal{F}(A)\cdot\mathcal{F}(B))
\end{equation}

With $\tilde{\mathcal{F}}$ being the inverse transform. This is the well known "convolution lemma". There is not much of a theory to see. In the Fourier domain, you just replace convolution by (point-wise) multiplication. Your question already contained the answer, to me it just appears that you were not sure about the details.