Place the stained gel on a UV transilluminator if it was stained with ethidium bromide. Place the stained gel on a white light box if it was stained with methlyene blue.
Turn on the illuminator and identify the length of the DNA samples in the ladder lane.
Compare the samples in the first lane to the closest DNA sample in the marker ladder. Extrapolate this information to give you an approximate length of the DNA samples in this lane.
Repeat Step 3 for each different lane that has a DNA sample.
Compare the lengths of the samples in each well to each other to find similarities.