Need understanding on - Network formula + some nested formula's

[VBABEGINER]

Dear All,
Can any one pls explain me how this formula works..

=(NETWORKDAYS($AF2,$AG2,Lookup_table!$J$2:$J$10)-1)*("19:00"-"7:00")+IF(NETWORKDAYS($AG2,$AG2,Lookup_table!$J$2:$J$10),MEDIAN(MOD($AG2,1),"19:00","7:00"),"19:00")-MEDIAN(NETWORKDAYS($AF2,$AF2,Lookup_table!$J$2:$J$10)*MOD($AF2,1),"19:00","7:00")

*Lookup_table sheet = J2 - J10 = holiday list
*AF = start date
*AG = close date

Pls explain..