3rd person singular uses heeft, have a look at the conjugation of hebben: http://www.verbix.com/webverbix/go.php?D1=24&T1=hebben
There are no steady rules for most words, except for:
• all plurals take de as a definite article.
• all diminutive singular nouns take het as a definite article.
Other than that, there are some guidelines you can follow, which you can read here:
And there's an app you can use to check which article to use when in doubt (it also has the guidelines):