After Jenkins server installation, it will be accessible at http://hostname:8080 address, the default anonymous user is present with full access. Obviously this is not ideal and you will want to have control over who has rights to access Jenkins instance and do necessary stuff.
Adding new Jenkins user ( and disabling anonymous ) is quite easy. In Jenkins web interface, follow Manage Jenkins -> Manage Users and add there desired user(s). After this, all you need to do is to fix permissions users will have
Manage Jenkins -> Jenkins’ own user database -> Project-based Matrix Authorization Strategy and fix there what you want for specific user to do. Do not forget to take away default rights for anonymous user!