Google Analytics:

Its a free & powerful tool to monitor traffic of your website, blogs and media pages.

Metrics:

Metrics is a measurement tool of Google Analytics like measurement of visitors, pages/visitors, average time on site etc..

Metrics can be seen as like graphs, comparison graphs of two metrics.

Metrics has one more option in the shape of Adsense tabs which can help to see revenue, average value, e-commerce, conversion rate etc..

Dimensions:

Dimensions is a tool to get information in the shape of table mostly in which we can monitor city to city visit, visit by browsing software, visit by computer or mobile etc..