A dataset is a simple collection of data, usually presented in a table. You can use a dataset as the basis for your story, and as a data source for Smart Predict.
Datasets complement models. Datasets are more suitable for ad-hoc analysis, while models are more suitable for governed-data use cases.
If you're not sure whether to use a dataset or a model for your story, this might help you decide: Models vs. Datasets.
If you're more interested in models, not datasets, see Models.