howdy jaunuolis,
danielle is from france so her english isn't perfect.her mentioning of the clay substrait is refering to the original soil and that it is retaining too much water (clay dirt based )
you need some kind of soil mixure that drains very quickly( gravel based) with pine bark added for a little water retention.cactus soil works if bonsai soil is not avalible.
as for tieing to the pot it may already be. its tough to explain how to do it, but it is wired trough the bottom hole and tied to the trunk or root ball