I have a form for member registrations that after submitting it, it takes some seconds to a minute depending on inteernet link. during these period, The browser just spins but I want this spinning be acompanied with a message like 'please wait while we process...'. How can I do it?

you could use a blanket and a small popup at the center saying 'Please wait..'
while the code is in progress.
Alternatively you could create a small heading like div with jquery with a timeout option. it should load till the rest of the html in the page loads and once the entire page loads after few seconds the heading at the top would disapear.

Most people would include an animated gif so that it appears that some type of processing is occurring. You could display a static message but that would also confuse users if nothing is happening on the screen. They will still believe the app is hung.

I prefer something with movement. I no longer use animated gifs because sometimes they don't work/display properly.

I now use spin.js in my projects. Its a spinner, but generated via javascript.

What you do is that when the submit button is clicked, start the spinner. Since there will be a page refresh at some point, you don't have to worry about stopping the spinner. If the page was incorporating AJAX where you aren't refreshing the whole page , then you can use the stop methods to control when to start and when to stop the spinner.