I am a beginner.

Com1:
IP 200.200.200.200
Mask 255.255.255.0
Gateway 200.200.200.1

If I want to add a router infront of Com1 with out bridged and keep the Com1 net setting.
How can I achieve this ? Thank you !

you need another subnet to _route_ it thru. Many times you will have a /30 subnet for the WAN, and then route the 200.200.200.0/24 thru that /30 range. Or you have to nat it.

Do you mean I need at least two set of IP to achieve this ?
Where can I do that in Router OS (/ip route) ? Thank you !