That number is an ip address. If you know of good & reliable ultrapeers to connect through & know their ip's then you can add them in that window.
An ip address is usually 4 blocks of numbers. eg: 106.201.84.31
ip addresses that start with 192 or 10 are always network numbers either from home or at work (& are not properly configured). They are impossible to use the LW direct connect function with. Not sure how they behave as ultrapeers, but safest not to choose one of those.