Adding an Instance
MultiMC allows you to add so called instances, they represent independent Minecraft installations and are the main use case of MultiMC. There's various ways to create new instances via the various platform integrations.
Straightforward... Vanilla! You can select the version you want. (The starred version is the recommended version) You can also select snapshots, betas and other miscellaneous official versions.
Allows you to import MultiMC instances from online or local Zip files and also supports some of the modpack platforms like CurseForge. More information about on the dedicated wiki pages Import Instance and Export Instance.
Integration with various third party platforms can change over time, generally you can search for modpacks and install them using various filters.