Intent filter location

I'm new to Android, so I'm sorry if this is a basic question. I'm reading documentation on Common Intents and it says to add an intent filter. I've tried to look through all the folders of my project, but can't seem to find any folder that says "activity", "filter" or "manifest". Obviously I'm not looking in the right place. So my question is, if I'm making an app to send an email and I need to add this intent filter, which seems to be a XML code, where do I add it?

<activity ...>
<intent-filter>
    <action android:name="android.intent.action.SEND" />
    <data android:type="*/*" />
    <category android:name="android.intent.category.DEFAULT" />
</intent-filter>
<intent-filter>
    <action android:name="android.intent.action.SENDTO" />
    <data android:scheme="mailto" />
    <category android:name="android.intent.category.DEFAULT" />
</intent-filter>

Thanks for your help.