I am on the train. (this could also be translated as "am sitting", but in Dutch this phrase could be used even when one were actually standing)
(intransitive, with te and another verb's infinitive)Used as an alternative to zijn + aan het to form a continuous aspect. Although it carries an implication of sitting, this is vague and is not strictly required or emphasized.
Terwijl jij rustig je tijd neemt, zit ik hier voor niets te wachten.
While you're taking your time, I am waiting here for nothing.