RDF can be expressed in a variety of different serialization formats. It can also be used inline with HTML. Following is an example of the most widely used of these formats so that you can compare them at a glance.
An XML-based syntax for RDF graphs that was the first standard format for serializing RDF.
See also: RDF 1.1 XML Syntax
A compact, human-friendly format.
See also: Turtle - Terse RDF Triple Language
A very simple, easy-to-parse, line-based format that is not as compact as Turtle.
See also: RDF 1.1 N-Triples
N3 (or Notation3)
A non-standard serialization that is very similar to Turtle, but has some additional features, such as the ability to define inference rules.
See also: Notation3 (N3): A readable RDF syntax
a JSON-based serialization (for Linked Data).
See also: JSON-LD 1.0
Not really an RDF syntax, but rather - a compatible format. "RDFa is an extension to HTML5 that helps you markup things like People, Places, Events, Recipes and Reviews. Search Engines and Web Services use this markup to generate better search listings and give you better visibility on the Web, so that people can find your website more easily." - rdfa.info
See also: RDFa
Also not really an RDF syntax, but a compatible format. This mechanism allows machine-readable data to be embedded in HTML documents in an easy-to-write manner, with an unambiguous parsing model.
See also: HTML Microdata
RDF Converter Services Online
There's a few decent RDF converter services that you can use online: