As Ankit Parmar said, you can check
Skip Base URL Validation Before
... but later you may run into problems. This message appears, probably because your domain is not public or inaccessible. If you skip checking the base URL, you can complete the installation, but you may get a strange problem with the ability to log in, but not to access the administration section (redirect to the login page without any error message, even if you see You are logged in by viewing the URL).
Instead of installing Magento under a local host, you should add a fake domain name to your host file and configure vhost accordingly. You can reinstall Magento by accessing the fake domain name in your browser. You can configure the domain name in the core_config_data table if this is not done.
More here: https://magento.stackexchange.com/questions/39752/how-do-i-fix-my-base-urls-so-i-can-access-my-magento-site