Temporary folder to a setup script

I'm creating a bash script which will download, run and remove a bash script.

I'm thinking to use the /tmp

Which temporary folder could I use to it?

The easiest to create a unique temporary folder is to use mktemp:

my_tmpdir=$(mktemp -d)

This will generate a unique name (e.g. /var/folders/8b/mn2vgjs42gs83krfy1fwxwb80000gp/T/tmp.LYnaqveK), create the directory with that path automatically and assign the path to my_tmpdir.

What I usually do within shell scripts or functions is

function do_stuff() {
    local t=$(mktemp -d)
    trap "rm -rf $t" RETURN
    (
        cd $t

        ## do stuff
    )
}

This will run the whole script in a temporary directory, it will also make sure that the directory is removed again afterwards.