Default page after login

You have to make a custom login block/page.

Check out the way that the forwarding is done in the default login block: in user.module, the login form is created by the user_block function ($delta=0). The line of interest to us is:

$output = form($output, 'post', url('user/login', drupal_get_destination()));

The third argument to the form function is the "action" parameter of the HTML form tag - the URL to which the form will be submitted. If you pay attention, you see that it is compiled from 'user/login' and the return value of drupal_get_destination().

The drupal_get_destination() function returns a string containting an element destination=query_string This argument is then used in the user module after the user is authenticated, in a drupal_goto() statement.

Now to answer your question, all you should have to do is create a new login form somewhere, with the line

$output = form($output, 'post', url('user/login', drupal_get_destination()));

changed to something like

$output = form($output, 'post', url('user/login?destination=path_to_page_you_want_to_go_to_after_login')));

If you want to do something more complex like redirecting the user based on roles, then the best way is probably to create a php script at the location that you redirect them to, that checks what roles the user belongs to and redirects them accordingly with another drupal_goto

Hope this helps.. sorry if its a little techincal, but what you are trying to do is not trivial.. you should be able to find documentation on this site about each of the individual steps of this process, but if you have problems feel free to ask here again

While you could do this by modifying user.module you can also do it with a module and make it more flexable in the process.
I have a module (4.5 and 4.6) that allows the administrator to define a login destination per role plus a rule for the page to displaying after logging out.

take a look at Front Page module. You may also find Sliced Bread PHP Snippets interesting.

nice code samples