A modpack is a ready-made set of mods, configs and recipes put together by the author so that everything works together. Building a set like that by hand takes ages: mods clash over versions, need libraries and handle game mechanics in different ways. A modpack has already done that work for you — all that's left is to pick the game version and loader.
A modpack is not only for your own game: you can also run it on a server to play with friends. Next to Install on a modpack page there is an On a server button: it installs the same modpack on a Millida Hosting server together with the right core, and a copy of the old world is kept in backups. Your friends install the modpack in the launcher and join the server address — everyone gets the same version because it comes from one place.
Each modpack here is one page with every released version. The card shows which game version and loader it's built for, how big the archive is and who the author is. Modpacks aren't installed like individual mods: click “Install” and Millida Launcher downloads all the modpack's mods, the right loader and Java, and creates a separate profile for it without touching your others. Mind the memory requirements: heavy tech-and-magic modpacks need six gigabytes or more and simply won't start on the default two.