The W3C Rule Interchange Format (RIF) is a forthcoming standard for exchanging rules among different systems and developing intelligent rule-based applications for the Semantic Web. The RIF architecture is conceived as a family of languages, called dialects. A RIF dialect is a rule-based language with an XML syntax and a well-defined semantics. The RIF Basic Logic Dialect (RIF-BLD) semantically corresponds to a Horn rule language with equality. RIF-BLD has a number of syntactic extensions with respect to traditional textbook Horn logic, which include F-logic frames and predicates with named arguments. RIF-BLD is also well integrated with the relevant Web standards. It provides Internationalized Resource Identifiers (IRIs), XML Schema datatypes, and is aligned with RDF and OWL. This paper is a guide to the essentials of RIF-BLD, its syntax, semantics, and XML serialization. At the same time, some important RIF-BLD features are omitted due to the space limitations, including datatypes, built-ins, and the integration with RDF and OWL.