!!!URGENT!! convolution problem

a signal x(t)=delta(t) is filtered by the filter f(t)=u(t)-u(t-1) multiple times.
*compute and plot the result of the first and second application of the filter.

>>i know that the output of a linear system is convolution of the signal with the filter. and for example i know the rule that says: y(t)=integral of delta(T)f(t-T)dT

in my cse here im confused how can i interpret this rule by having a shifted unit step function???