If you are launching a brand new website or Google was penalize your website and now you are planning to re-launch new website with fresh content, new design, layout and everything. Then you must inform to google after your new website will go live. Most of the times Google search engine bot (Googlebot) will automatically crawl your new website or web pages but if you being penalized by Google then you must do following step to re-crawl or re-submit your website to Google.
1) Log in to your Google Webmasters Tool for your website
2) Click on Crawl option then you’ll find more options in crawl
3) If you wish to crawl home page then don’t write anything inside the box but if you want to crawl internal pages then add specific page URL. about-us.html, contact.php etc
4) Then click on Fetch as Google button
See attached screenshot for all steps. Once you clicked on Fetch as Google you will find your link will appear in the table. Status success means Googlebot successfully fetch your web page but if error will come then there is might be issue with your server response time or any other issue. For server response time you must contact your hosting service provider.
Now you can submit your web page to Google. Click on Submit to index button then Google will ask you do want index only one URL or URL and all linked pages too. Select one option then click on ok button. You’re almost done here. After some time Google will be index your web pages.
Note: If your website has been violated Google guidelines or Google has been penalize your website or specific web pages then you need to submit reconsideration request to Google using your webmasters account. After submitting request to Google then they will contact you soon for the same.