I am creating new header.phtml and footer.phtml and store into app/design/frontend/<vendor_theme>/mytheme_name/theme_layout/template/html
.
so how to add new header and footer in magento/blank theme.
You can overwrite the existing templates by copying them into your theme and making changes to the template files.
So copy these two files:
vendor/magento/module-theme/view/frontend/templates/html/header.phtml
vendor/magento/module-theme/view/frontend/templates/html/footer.phtml
Into your theme:
app/design/frontend/VENDOR/THEME/Magento_Theme/templates/html/header.phtml
app/design/frontend/VENDOR/THEME/Magento_Theme/templates/html/footer.phtml
Change in xml
<default>
<reference name="header">
<action method="setTemplate"><template>page/html/Your_Custom_Header.phtml</template></action>
</reference>
<reference name="footer">
<action method="setTemplate"><template>page/html/Your_Custom_Footer.phtml</template></action>
</reference>
</default>
And
Placed Your_Custom_Header.phtml and Your_Custom_Footer.phtml in theme directory
app\design\frontend\Your_Theme\template\page\html\ Here