"How do you feel today?"
Translation:¿Cómo te sientes hoy?
When do you use 'tu' and when do you use 'te'? I used 'tu' and it said I was wrong...
In this case, the verb sientes is being used reflexively. This means that "you" is both preforming and receiving the action of feeling. Reflexive verbs are always immediately preceded by the appropriate reflexive pronoun, in this case "te". More information can be found here:
Without te, you would be asking "what are you feeling?"
Q: Qué sientes hoy?
A: Hoy siento mí gata. Ella es muy esponjosa!
' Sentirse' is a reflexive verb meaning, in effect, 'to feel TO oneself'. Hence you need the object form of the pronoun 'te' and not the subject form 'tu' when saying, ' how do you feel (to yourself)..'?
Would having tu after sientes be wholly incorrect here or add emphasis as in "how do you yourself feel today?" Not that one would phrase a question like that often, just curious if it would make grammatical sense at all en espanol.