how to tag the Vlan and Configure trunk

[Kavinrajhen RA]

HI all, I am having Cisco Router 2911 with 3gi port,Firewall NSA3500 connected to gi0/0 in router and 2510g-24 X 2 Nos. Connected to gi0/1&0/2,we have created VLan in 2 Nos. in gi0/1 which will be conneting to DMZ and Servers. the gi 0/2 in that 6 VLans which will connect to all the departments and i want to know how to enable in one switch multi trunk port and from there i will connect to 1800 switch. i am having totally 20switch of 1800.kindly how configure trunk port and configuring the vlan