There are videos that will explain how to do it. It may be for versions prior to the one you want to play but there isn't much difference.
I recommend getting started with server hosting by using Hamachi. Hamachi is a program that creates a VPN, which stands for virtual private network. Other computers can join this network with hamachi and connect with you by tricking the computers into thinking you're in a local area network (LAN)
You can download the server files for your desired modpack from the launcher. From there, you'll be given everything you need to start your server after installing hamachi by using the start.bat file which will bring up a command prompt that'll show you the server's loading progress. Once it's done you exit the command prompt and open the server.properties file that was created in the process. Type in your hamachi ip address after serverip= and make a note of the query port number. You can change this if you like. Run start.bat again after saving the properties and then you should be able to connect to the server using the ip address followed by a colon then the queryport, it should look something like 5.255.35.16:25565 or something to that effect.
If you have trouble, or your friend can't connect but you can, try to find video tutorials on hamachi servers or direwolf server installations and make sure that your firewall has hamachi enabled. This goes for your friends too!
Hope this helps!
