You sit down = Usted se sienta/te sientas (formal, informal)
You sit (i.e. 'are seated') = Usted esta/tu estas sentado
La maestra te está enseñando sentarte.
sentarse
Sientate
'Desk' in Spanish is 'escritorio.' It depends on what kind of desk. A large desk, such as a teacher or businessman might have would be called an "escritorio" as mentioned above. A smaller desk, such as a High Schooler would sit at is called a "pupitre" or "banco" depending on the country.
As a part of my job evaluation, I must sit down with my boss and discuss everything that I have done in that year.
It is said "Puedo sentarme a tu lado?"
"To feel" is the verb "sentir". Do not confuse this with "sentar", which means "to sit".
Sentar is the Spanish verb for "to sit". If you are asking someone to sit down, you would say "Sientese, por favor."
I would use "instruct" in a sentence like this: "The teacher will instruct the students on how to conduct the experiment."
to sit = sentar or tomar asiento
Me gusta sentar en la sección no fumar.
because the teacher sat her there
ask your health teacher to say something