Going to give the short version.
1st, you probably didn’t distribute the “Run First (Runtime Files Needed to run the Engine).exe” file. They all need to get a copy of that from downloading EO4 here or from you and run it first.
2nd, to allow people to connect to you remotely it takes several steps. You need to launch your server, I am going to assume you are using the default port of 7001 if not, everywhere I refer to 7001 replace with the number you chose.
Localhost refers to your machine or the machine that you are on so if they try to connect to localhost it will not work since they are not the host therefore you have to give them your public IP. Your public IP can be determined by going to www.ipchicken.com
After you have your public IP launch your client, click new on the server list. For the host put your public IP, for the port 7001 and try to use that server. There is only a 10% chance that it will work. If it does work then great, you are done tell your friends the public ip, port and tell them to install the runtime files and they should be good.
If it does not work like it shouldn’t then you need to forward ports on your router to allow the incoming traffic. Every router is different so I cannot tell you exactly how but Youtube videos will give you the gist of how to do it and then on this site it will let you select your router brand and give you step by step instructions on how to do it.
After you port forward you can try to connect again using the public ip option in the client, if it works then great if not then come back and give us some info including your port number, your router brand/model, your public IP, your private IP (on top of the server window) and a screenshot of your routers port-forward page with your changes and then we can tell you what is right/wrong.
P.S. Your personal computer should be fine to host 5-10 people at least. ;)