Hi Bala,
Below are the answers to your questions:
Metrics - A metric is a structure that specifies the type of event data captured in the report (more details - https://marketing.adobe.com/resources/help/en_US/reference/metrics.html)
eVar - The eVar variables are used for building custom reports (for conversion)
prop - Property (prop) variables are used for building custom reports within the Traffic Module
Dimension - It define as “a component or category of data. Metrics (counts and ratios) are measured across dimensions.” Dimensions can be a variety of attributes such as search engine, country, page, referring domain, date/time, keyword, etc. Dimensions are expressed as textual values. For example, California, Utah, Virginia, and New York would be textual values of the US States dimension
Hope this helps.
Best,
-Suhail Parkar