Hi, I'm new in Mathematica, i have some experience using Maple, so now I'm testing Mathematica, but is there any help command? I mean like an index where I can search for example how to solve an equation (I know that is with the command Solve), but where can I find all the commands? Another question is what is the browser plugin?
The same documentation you get within Mathematica using the Help > Wolfram Documentation menu selection you can find on-line at http://reference.wolfram.com/language/.
Moreover, don't overlook the many screencasts and other resources you can reach from http://www.wolfram.com/support/.
The browser plugin is so that CDFs (for example items from http://demonstrations.wolfram.com can be active in a browser.
Under Help choose Wolfram Documentation.