How do I create a .deb file?

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http://askubuntu.com – Yes, I know that this question has been asked many times before, but none of the answers really helped. I'd like to package the Minecraft launcher (which has no proprietary code, AFAIK,) into a .deb file so that I can put it on a flash drive and share it with my friends. I have managed to install Minecraft it manually (put some files into /opt/minecraft, download an icon, and create a .desktop file in /usr/share/applications,) and I have made a shell script that completely automates the process, but it relies on wget to retrieve a few files, including the .desktop file. (It isn't a self-extrac (HowTos)