Define it as a function:
f = @(x,a,b,c) a*exp(-(x-b).^2)/(2*c^2);
then define your constants a, b and c, specify the range of values of x, call the function and plot the results. For example
a = 1; b = 2; c = 3;
x = -2:0.1:8;
y = f(x,a,b,c);
plot(x,y)
