What is the relationship between BioSamples, SRA Experiments, Runs and my data files?

BioSample is descriptive information about the biological source materials, or samples, used to generate experimental data in any of primary data archives.
Please see Sample granularity.

Each SRA Experiment is a unique sequencing library and sequencing method for a specific sample. Importantly, much of the descriptive information that is displayed in the public record of your data is captured at the level of the DRA Experiment.

SRA Runs are simply a manifest of data file(s) that should be linked to a given sequencing library – no information present in the Run is displayed on the public record of your project.
Note that all data files listed in a Run will be merged into a single SRA archive file (and fastq file for distribution).