what is sientese?
I did not find it in dictionary or translation
4 Answers
As mentioned it means 'sit down' when given as a command.
And if you want to be technical it's the usted form.
Siéntese en el piso. Sit on the floor.
Here's the tú (informal) form for comparison.
Siéntate en la esquina. Sit in the corner.

It means sit down. Siente is the usted form of the imperative of sentar and the se at the end is just a just a pronoun.
And it should be "siéntese", with an accent over the first "e".
It means "Sit down"