How can I create custom contribution page (CiviCRM 4.7.25 on Wordpress 4.8?)
Can you please edit your question to add your CMS and CiviCRM version. Depending on your CMS there may be other options for customization.

The yellow section only appears when a user is logged in to the site. It is designed to prevent a user from overwriting their information with another if they are entering a contribution on another person's behalf. I would recommend leaving it there to avoid accidental data changes. You could add some custom CSS to change the look. 

As for the form itself and the pricing section you may want to review the information here which is an overview of the contribution pages: https://docs.civicrm.org/user/en/latest/contributions/online-contributions/

Also reviewing the following two sections on profiles &amp; price sets can be helpful.

Profiles: https://docs.civicrm.org/user/en/latest/organising-your-data/profiles/

Price Sets: https://docs.civicrm.org/user/en/latest/events/complex-event-fees/#price-sets

Hope this helps.