You already mentioned just connecting the photocell to an ammeter -- that should work fairly well for your first tests. The output of the photocell is a photocurrent that depends on the level of illumination (and the wavelengths of the incoming light). The current flows out of the cathode of the photodiode / photocell. So connect the + lead of your DVM in "mA" setting to the cathode of the photocell, and the - lead to the anode of the photocell. If your DVM's current measurements are sensitive enough, you will be able to plot a couple decades of photocurrent variation as you move the cell closer and farther away from the light source.

A better test circuit would be to use an opamp to make a current-to-voltage converter, and measure the output voltage. I'll leave that as an exercise for the reader for now....

As berkeman has already said you can use an ammeter. Basically, you need to connect the positive lead from your ammeter to the cathode of the photodiode and the earth or negative lead to the anode of the photodiode. This will allow you to measure the rate of flow of electrons, which is proportional to the illuminiation of the photodiode (and dependant on the wavelength of light). If you plot current against distance from source, you should be able to determine a relationship between the two variables.

However, it is more useful to measure the voltage.

If you haven't used op-amps before then it is probably best to just measure current. The op-amp basically converts the current produced by the photodiode into a potential difference, a large resistance is used to prevent a significant current flowing, thus obtaining a more accurate value for the potential difference.

A basic circuit diagram can be found here ; http://www.wam.umd.edu/~toh/ElectroSim/Photodiode.html