Set parent and child

Hi,

i have 2 different content types (just call it contenttype1 and contenttype2),

contenttype1 get "can be parent" checked
contenttype2 get "can be child" checked

when i create a content, for example i create "content1" with type content "contenttype1", and then i create another content, "content2" with content type "contenttype2".

how can i tell drupal that content1 is the parent from content2 and?
which function do i should use?

i know this is a basic question, but plz help me.