Basic Installation of RouterOS
This example shows how to install and configure Mikrotik RoterOS.
First download new RouterOS form here 
Then write ISO image file to CD and put in CD-ROM Drive and turn on.
Press "a" key for select all and then press "i"
Answer "n" to first question and "y" to second
after rebooting type "admin" as login and no password.
Add IP address
When mikrotik prompt is ready assign IP address to NIC:
/ip address add address=10.0.0.1/24 interface=ether1 add address=192.168.0.1/24 interface=ether2
ether1 = WAN ( Connected To Your Router ) Alone -- ether2= LAN ( Connected To Your Switch (hub) With Clients -- now add default gateway IP address:
/ip route add gateway=10.0.0.2
10.0.0.1,192.168.0.1 and 10.0.0.2 is sample data and you should use your IP for setting
if use your IP now you can ping internet
ping 188.8.131.52 184.108.40.206 64 byte ping: ttl=242 time=255 ms 220.127.116.11 64 byte ping: ttl=242 time=243 ms 18.104.22.168 64 byte ping: ttl=242 time=247 ms 22.214.171.124 64 byte ping: ttl=242 time=243 ms 4 packets transmitted, 4 packets received, 0% packet loss round-trip min/avg/max = 243/247.0/255 ms
NAT will use until client with invalid IP connect to internet, so we must run NAT on mikrotik and set client IP in range of 192.168.0.2 and set client gateway to 192.168.0.1(Secend NIC of mikrotik)
/ip firewall nat add chain=srcnat action=masquerade out-interface=ether1
this will be route all traffic to interface 1 that have an valid IP so will be NAT and go to internet