If you have not used Bluetooth Low Energy before there are a few things to know before you start.
1) BLE is not a lower power version of Bluetooth "Classic", it is a different type of interface. If the other board you have is not BLE capable then you will not be able to connect them. If the Nordic app can see both then you are probably OK.
2) BLE connections need one "peripheral" device and one "central" device. Typically a smartphone is a central, and a fitness tracker is a peripheral. Right now, the Arduino 101 can only be a peripheral device - so the other board will need to be a central and it will need to initiate the connection. As a peripheral device, the Arduino 101 cannot initiate a connection.
If the other board can be a central device, you need to make it scan for the Arduino (identify it by MAC address or the name given to it in your sketch), and connect to it if available. That's it. Your Arduino 101 will need to be advertising itself to be available for connections. There are no pairing codes etc needed, the connection should just succeed.
If the other board you have is a BLE peripheral only, then you will need to wait for central mode to be enabled. (I guess central mode support will be released as an upgrade)