My homework ask to to graph the functions
f(x)=(1/5)^x
y=2(1/5)^x+3
etc.
How do I do this??

The same way you graph all functions: find the domain, calculate the limits towards the ends of the domain, calculate the first and second derivatives and find out where the maxima and minima are. Pick some reasonable points and calculate the functions there and draw all of this in your graph.