Launch

The multipass launch command without any argument will create and start a new instance based on the default image, using a random generated name:

$ multipass launch
…
Launched: relishing-lionfish

You can then shell into that instance by its name:

$ multipass shell relishing-lionfish
…
multipass@relishing-lionfish:~$ 

The full multipass help launch output explains the available options:

$ multipass help launch
Usage: multipass launch [options] [[<remote:>]<image> | <url>]
Create and start a new instance.

Options:
  -h, --help           Display this help
  -v, --verbose        Increase logging verbosity, repeat up to three times for
                       more detail
  -c, --cpus <cpus>    Number of CPUs to allocate.
                       Minimum: 1, default: 1.
  -d, --disk <disk>    Disk space to allocate. Positive integers, in bytes, or
                       with K, M, G suffix.
                       Minimum: 512M, default: 5G.
  -m, --mem <mem>      Amount of memory to allocate. Positive integers, in
                       bytes, or with K, M, G suffix.
                       Minimum: 128M, default: 1G.
  -n, --name <name>    Name for the instance. If it is 'primary' (the
                       configured primary instance name), the user's home
                       directory is mounted inside the newly launched instance,
                       in 'Home'.
  --cloud-init <file>  Path to a user-data cloud-init configuration, or '-' for
                       stdin

Arguments:
  image                Optional image to launch. If omitted, then the default
                       Ubuntu LTS will be used.
                       <remote> can be either ‘release’ or ‘daily‘. If <remote>
                       is omitted, ‘release’ will be used.
                       <image> can be a partial image hash or an Ubuntu release
                       version, codename or alias.
                       <url> is a custom image URL that is in http://, https://,
                       or file:// format.

The only, optional, positional argument is the image to launch an instance from. See the multipass find documentation for information on what images are available. It’s also possible to provide a full URL to the image (use file:// for an image available on the host running multipassd).

You can change the resources made available to the instance by passing any of --cpu, --disk, --mem options, allowing for more CPU cores, disk space or RAM, respectively.

If you want your instance to have a name of your choice, use --name. It has to be unique, two instances can’t share the same name.

By passing a filename to --cloud-init, you can provide “user data” to cloud-init to customize the instance on first boot. See their documentation for examples.