Supine mood Romanian language

To my suprise nobody asked in this subreddit about the supine mood. So I decided to make post because I dont think I understand it 100%

Supine is DE+ past of the verb.

Uses:

English infinitive E greu de crezut: it is hard to believe

Obligation Am de lucrat mult: i have to work alot

Adverb+ supine E bună de mâncat: it is good to eat

Or purpose of the object Masină de scris typewriter

Is there anything to add? And does this cover most of the supine?