Adding names and information to existing geography

Hello! I am kind of new to JOSM. I want to know how can I add name and other information to an existing geography.

There are these lakes in India, which someone has been kind enough to draw, but are not named. I would like to name them.

You can start at the OSM wiki → JOSM and read some instructions and tutorials,

or see … there are some JOSM related demo movies

thanks. Its easier and more intuitive via Potlatch to assign names to existing POI.