what actually the function for e(g,g)^xy

I doing a project using ABE "Attribute-Based-Encryption" but i didn't understand what actually the function for $e(g,g)^xy$. Just tell what's the calculation need to perform here. I gone through no of publications and thesis but i didn't understand this.

$PK = (T_1 = g ^{t_1} , ..., T_{|u|} = g^ {t|U|} , Y = e(g, g)^ y )$

Using the above values how can i calculate PK.