How to 'interpret' the Fourier Transform (specifically, of a convolution kernel)
Convolving a signal with a kernel is equivalent to applying a filter to it. The kernel is the impulse response of the filter, and the Fourier transform of the kernel is thus the frequency response of the filter.

In your case, the filter's impulse response is a rectangular function of width 2 and centered at 0. You can interpret this filter this way: for any $t$, the filter output $y(t)$ will be the average of the input signal $x(t)$ over the interval $[t - 1, t + 1]$. This is an averaging, low-pass filter, and indeed, the Fourier transform of the kernel is a decreasing function, showing that the higher frequencies are attenuated.