SAP is a business application to automate business process. Many industries use SAP to automate their business processes. It has very modules like Technical Programming (ABAP), Functional (SD - Sales and Distribution, FICO - Finance and Controlling, MM - Material Management), Portal (webdynpro) etc
There are various SAP courses available through authorized SAP vendors like ATOS, Genovate, Invenio Business Solutions, BPCL, NIIT. There is no eligibility for doing SAP course except that you understand English and have a sound knowledge of business process of SAP module that you are trained in.
SAP course does not guarantee a job. Though SAP is a huge market, people with no SAP experience find it difficult to nail jobs as companies prefer experienced people.