how to give edit permission content to new user in drupal? I have a content type called "company." I have uploaded a lot of company details to the site by myself. 

Now I want that people employed by these companies create new accounts in my site, and they should be allowed to edit the details for the company where they work.
I need to give the permission for editing the "company" nodes in my site to new users.

Can you tell me how to implement this?
If there is only a single user that will have permission for a given company node, you can assign them as the author of the company node and give them the "edit own company nodes" (or similar) permission.

If there are multiple, it's going to be trickier, you could for example add a hidden user reference field to the company node (which only you can edit, with a field permission module) and use http://drupal.org/project/nodeaccess_userreference. Or use http://drupal.org/project/content_access, which allows to configure permissions for single users directly.