OpenMRS is a flexible, modular, multi-layered system, and one of its strengths is that its platform can be used in many different configurations. As a result, "OpenMRS" can mean many things.
A particular configuration of the OpenMRS Platform, OpenMRS modules, and (optionally) other integrated applications, that can be installed and upgraded as a unit.
There are two ways to start using OpenMRS, depending on your needs and available resources:
Some of the advantages to using a distribution that already exists are:
An OpenMRS distribution that intends to serve the worldwide audience of clinics, hospitals, governments, NGOs, etc, who want a patient medical record for purposes of clinical care.
An OpenMRS distribution that is intended for a specific clinical or geographical use case, or a non-patient-care use case. For example, a standardized country specific distribution or one targeted at a specific disease epidemic.
A configuration of OpenMRS that is technically built like a Distribution, but is only intended for use by one specific consumer. If you are not the specific target of this distribution, you wouldn't probably use it directly, but as a developer or implementer you may learn a lot from studying or forking it. However, there may be opportunities to collaborate with the teams working on these distributions if you wanted to create a replica of their clinical and technical environments.
Maintained by the OpenMRS community, this distribution demonstrates how the platform's capabilities can be used to build an EMR. You could use this out-of-the-box as a facility EMR, but it (currently) doesn't have the complete EMR feature set.
Maintained by ThoughtWorks and the Bahmni community, Bahmni is an out-of-the-box EMR and Hospital Information System that can be configured without programming.