Now simply go to this site and download HUG-2.0 or use it online. It is
a transliteration based editor , which means you type "raam" to get
"RAM" in dewanaagari , or type "seetaa" to get "SITA" in devanaagarii.
More help is available there.
Use this editor and prepare your Devanagari text. Now copy the
Devanaagari text wherever you need , eg in the text box of gmail ,
text box of a Forum etc and send it.
Note that this is simplified information for getting started quickly.
If you have further problems , do let us know. Once you get started ,
you may yourself choose suitable Hindi editor for you . I will suggest
to go for Baraha 6.0