Namely I bought minecraft and I have a second pc and I thought if I could play with an acc with another person multiplayer or modpacks. I would be happy if it would work.
An account can't be online on two different machines. The session of one account expires when you log on to another computer.
You're then online with both accounts but you can't get to the same server because you're on it.
You can log in to both devices with your Acc, but if you try to connect with both on the same server, then an error message comes. So no, it will not work.
What a shame
No, it does not work because both the same session key is logged in and the server has a security inside if two identical IPs and same names are on it, either or luckily only one of them will be kicked.