Once you have worked through all of the previous steps you will have all you need to plot a Hubble diagram. A Hubble diagram is a plot of radial velocity against distance (see The Cosmiv Perspective p618, figure 20.20).
How do you get velocity from redshift? For the low redshifts of the objects you have been given, there is a simple relationship given by
radial velocity = redshift × speed of light
Given that the speed of light is 300,000 km/s (a close approximation! - see The Cosmic Perspective Appendix A), for each of your galaxies you can calculate the radial velocities.
For example, if you have a galaxy with a redshift of 0.025, then the radial velocity is given by
radial velocity = 0.025 × 300000
= 7500 km/s
You can draw the graph for your Hubble diagram by hand, or if you know how to, you could use software like Microsoft Excel to plot the graph for you. You should plot the galaxy velocities in kilometres per second against their distances in millions of light years. To make plotting easier there is a blank graph available for you to download here (download graph (pdf format)); you can print this and use it to plot your data points.
Once you have plotted the data for your five galaxies, you need to draw a straight line through them. Unless you have been very lucky you won't be able to draw a line that goes exactly through all the points, but you want to draw a line that goes as close to as many points as possible. The line should also go through zero.
This line allows you to make an estimate of the Hubble constant. The Hubble constant is the gradient of this line, so you need to calculate the gradient. With the units used on the graph linked above, the Hubble constant is in terms of kilometres per second per million light years (MLy); see The Cosmic Perspective p 618-619.
Now that you have the Hubble constant you have almost finished. One simple thing we can do with the value of the Hubble constant is estimate the age of the Universe. Read The Cosmic Perspective Mathermatical Insight 20.4 (p621), and calculate the age of the Universe from your value of the Hubble constant. How does your result compare with other ages given in The Cosmic Perspective? (Your answer may possibly be somewhat different, depending on the galaxies that you have been allocated.)