BEL has three levels: terms, statements, and script. Terms represent physical/abstract entities like genes, proteins, complexes, and phenotypes; statements represent the relationships between terms; and scripts organize groups of statements with their annotations such as the citation for the publication reporting the observation, or the context in which the observation was made (e.g., species, tissue, cell line). Script also contains document-level metadata about the curator, references to external vocabularies, and provenance.

The first part of this tutorial will focus on writing biological entities as BEL terms, then how to combine them into relations. After, it will go over using annotations and finally how to group them all together in BEL Script with appropriate metadata.