You need to have an independent variable (e.g., when plotting y vs. x, x is the independent variable). So if you want to plot epsilon against some other variable, that other variable needs to change. Here's some code that might do what you want.
M=1; N=2; E=3; sigma=2; n=2; t = 0:0.01:10; %this means have the variable t start at 0 and move in increments of 0.01 until it reaches 10 epsilon = M*sigma.*(1/E + t/n) + N*sigma.*(1-exp(-E.*t/n)); %the meaning of ".*" is that we multiply against each element of the vector t