What is a Pattern?
Patterns are parameterized collaborations; that is, they are a group of collaborating objects/classes that can be abstracted from a general set of modeling scenarios. Patterns are an excellent means of achieving re-use and building in robustness. As patterns are discovered in any new project, the basic pattern template from previous engagements can be re-used with the appropriate variable names modified for the current project.
Patterns generally describe how to solve an abstract problem, and it is the task of the pattern user to modify the pattern elements to meet the demands of the current engagement.
Sparx created GoF Patterns
To get you started with Design Patterns in Enterprise Architect, Sparx Systems provide you with a zip file containing the patterns described in the book Design Patterns - Elements of Reusable Object-Oriented Software by Gamma et al., referred to as the 'Gang of Four' or GoF. Download this zip file of the Gang of Four patterns for Enterprise Architect from the links below.
When you have downloaded and unzipped the file, you can import the GoF Patterns as described in Import Patterns.