Question about hooks

Trying to learn how to write plugins, so this is my first go at this. I am doing this tutorial, and it tells me to call my function upon plugin activation like this:

register_activation_hook(__FILE__, 'my_plugin_activate');

Which does not work. What does work is this:
register_deactivation_hook( __FILE__, my_plugin_activate() );

What am I doing wrong?

Thank you very much for your help!