First you will need to decide which machine will fund the channel. In the current implementation only one party can lock funds to a multi-sig address. Let's say the machine that will fund the channel is A and the other is B. Now open the c-lightning in the terminal on machine B and type
lightning-cli getinfo. It will give you a bunch of information. Look for the
address. Then open the c-lightning on your machine A's terminal and type
lightning-cli connect id@address:9735. Where
address are the info that you got from the
getinfo command on machine B.
After connection has been established, you can then open the channel using the command
lightning-cli fundchannel id satoshi [feerate] [announce] on your machine A. Here
id is the node id of the node with whom you want to open the channel and satoshi is the amount of bitcoins in satoshis that you want to use to fund the channel. If you want to keep your channel private you can set
announce to false.
If you want to expose the node to the internet and use the internal IP addresses you can do so by adding
announce-addr=<public_IP> in the config files. You can also pass these commands in the terminal when starting the lightningd daemon, but it is easier to do it in config file so that you don't have to do it everytime you start the daemon.