"Si es, es" is Spanish for "If it is, it is". If you just mean "si es", that means "if it is". If you mean "Sí es" (with an accent on "Sí"), it means "Yes, it is".
"Si hoy es jueves, mañana es..." means "If today is Thursday, tomorrow is..."
si es porque means if it's because
"if it's not with you"
Si algo es "clinically proven," es probado por científicos.
If the party is everything.
if you have msn, mine is...
If the movie is very interesting..
Na es diminutivo de "nada". Nothing
What a sweet life it really is.
It translates to "if today is Monday, tomorrow will be."
tu es si belle et si sexy / tu es si beau et si sexy
He/she is a monkey.