"Stephanus feels well."
Translation:Stephanus bene se habet.
Surely "se" is not necessary? "Stephanus himself feels well" vs "Stephanus feels well"?
"Habet" means hold, not feel. The literal translation would be "stephanus holds himself well". Just like in English, hold can have a physical meaning and a meantal one ("we hold these truths . . . ). Another translation into english could be "I consider myself not well". Se is in the accusative form meaning it is the object of the sentence.
I'm not an expert in latin so maybe I'm wrong about this though.
You need to use "se" because it is necessary within the idiom, which literally translates here to "Stephanus holds himself well." You need to point out that the action is reflexive and not carried out on someone else. "Stephanus himself feels well" would be "stephanus ipse bene se habet." Ipse, which means himself in that sentence, is an intensifier.
Hope this helps.