Create new VCN
– it is preferable as a good practice.
You can use existing VCN but when you opening required ports you opening those ports for complete subnet – you want to control to what you opening to the public.
Enter VCN Name
Define CIDR Block – as in this VCN will be only one or two servers use small subnet ( good subnet calculator is at http://www.subnet-calculator.com/)
Create Subnet for this VCN
CIDR BLOCK – I am using this same as for VCN
Routing Table – you can have different routing tables but only one is active.
Select Public Subnet – you want this subnet to access from outside.