Review/Enter/create parent/child samples.  Use the Edit/Close Sample form and click on the Associated Samples Tab:

The associated samples tab allows you to link samples to maintain a relationship between the samples.  For example, when a water distribution sample comes back as Present, we need to do a Repeat, Upstream, and Downstream Sample.  In order to trace those samples back to the original sample, you would need to create those samples as Child Samples.