How to interpret the effect of different windows in short time fourier transform?
A widnow $w[n]$ truncates and weights (tapers) an input signal $x[n]$, to produce $v[n] = x[n]. w[n]$., for subsequent spectral analysis of $x[n]$. A windows's effect on the input signal's true spectrum $X(e^{j\omega})$ is described by a convolution of $X(e^{j\omega})$ with $W(e^{j\omega})$ (window's Fourier transform);
$$V(e^{j\omega}) = \frac{1}{2\pi} \int_{-\pi}^{\pi} W(e^{j\theta})X(e^{j (\omega -\theta)}) d\theta $$
due to this convolution, two main effects are observed on $X(e^{j\omega})$.
1 - smoothing (smearing) of $X(e^{j\omega})$ due to the main lobe width of $W(e^{j\omega})$,  which results in a loss of spectral resolution.
2- spectral leakage due to peak side lobe of $W(e^{j\omega})$, which results in a loss of weak components shadowed by nearby stronger ones.
Main lobe width of any window type is primarily determined by its length. Increasing the length of any window will therefore decrease its main lobe width (hence increase its spectral resolution capability)
A rectangular window has the narrowest main lobe width and the highest peak side lobe, compared to all other windows. And the remainig window types perform a tradeoff between mainlobe width and the peak side lobes.
Peak side lobe is primarily determined by windows's shape. So by changing the shape (type) of the window you adjust it's leakage amount.