Android Question How to access to device apps(contacts, sms...)?

Hi all,

i am new here and would like to develop my first android app. I'm trying to develop for myself an app-launcher with buttons, which forward to system app like contacts, sms etc.

For example: Can anyone show me how i create a button "Contacts" which after click forwards to system contact window?

I'll appreciate any help of u.

Best regards,
Leo