So I am trying to select an option from drop down list so that it should only show the info path form related to that particular section
in InfoPath form, we have concept for
formatting rules, which is used these task. You can add
formatting rules to show/hide form components.
There is a very good documentation by MS on same. Follow the URL to learn more. https://support.office.com/en-us/article/Add-formatting-rules-C9171387-0061-43CC-9D54-E260A6B8F9A9