Parameters
The three parameters in an equation of the form
y = b0 + b1 x + b2 z
are interpreted in a similar way to the corresponding parameters for an equation with one explanatory variable.
Illustration
The diagram below represents a linear model. The diagonal grey line that is initially visible shows how y is related to x only.
The two red arrows that are initially visible represent the parameters b0 and b1. Adjust these parameters by dragging the arrows vertically. Observe that b0 is the y-value when x=0, and that b1 is the increase in y when x increases by 1.
Now drag the centre of the diagram a little towards the bottom right to rotate the diagram (or click the x-y-z button). A third arrow becomes visible that allows you to change the third parameter. Adjust all three parameters and observe how they affect the positioning of the plane.