The document defines the unit step function and shifted unit step function. The unit step function u(t) has a value of 0 when time t is negative and a value of 1 when time t is positive. This represents flipping a switch. The shifted unit step function describes waveforms that are applied at times other than t=0, using the unit step function delayed to the specified interval. The document also mentions the Laplace transform of integrals, derivatives, and its use in solving differential equations and initial value problems.