UML is a modeling language used in software engineering that helps by providing a standard and organized way to visualize the design of a system. It was created with the intention of standardizing the diverse notational systems of software design.
Large applications must have a great structure so they can work succesfully under stressful conditions; they should enable scalability and high level security. Also their structure should be simple enough so that any programmer can be able to address any given problem within the code without having to learn how to give specific maintenance to that certain piece of code, also it enables code reuse.
UML’s capability to adapt allows you to use it in code programmed in any type of programming language, operating system, combination of hardware and network. It is specially useful in languages such as C++, Java and C#; but it works as well with COBOL, VB or Fortarn.
“Some tools on the market execute UML models typically in one of two ways: some tools execute your model interpretively in a way that lets you confirm that it really does would you want but without the scalability and speed that you need in your deployed application. Other tools […] generate program language code from UML, producing most of a bug-free, deployable application that runs quickly if the code generator incorporates best-practice scalable patterns […]” (Object Management Group, 2005).
With UML you can model:
– Structure Diagrams
– Behavior Diagrams
– Interaction Diagrams
If you want to start a UML based project you have to follow 3 simple steps:
1.- Select a Methodology (There are many types of methodologies; there are probably some that fit with what you want to do but others that don’t. It is important to pick the right one)
2.- Select a 
Development Tool (some UML tools are used for some specific methodologies)
3.- Get training (ask for help if you’re not familiar with the methodology you’re about to use)
REFERENCES:
Object Management Group. (July 2005). What is UML. Unified Modeling Language. Recovered from http://www.uml.org/what-is-uml.htm
