Its the same as every other module - the root of your silverstripe installation. Eg the folder which already has sapphire, cms etc.
So your structure should be the following. Note if you download using the automatic download generator (or trac) it throws some version numbers in the filename or adds another needed level which needs to be removed
I'm new to SS and this is just throwing me totally - is there not just a folder called addons that all the addons should just be installed to?
I am personally for a dedicated 'modules' folder so its easy - copy to modules/ and done. But some reasons why people don't want a simple solution like that. You can find discussions on the forum about this structure debate and on the dev mailing list.
Thank very much Willr - I actually had it in the correct place at one point, it's just that when I tried to change an existing page to a user form, it said 'this will change once saved' but then it always reverted back, which made me think I had something wrong!
I did have a weird problem, when I pressed 'add' button I just got a blank page (http://domain.com/index.php/admin/EditForm) - but pressing back let me use the form ok.
Now when I save and publish the form, it just appears on my page like this:
Generated with the default ContentController.ss template
Is there something else I need to do to get it to display and use my template? Do I need to create a new page template or something? Sorry to be a pain, but the documentation seems to suggest it should just work