I have no idea what soil my plant needs...I have to prepare mix for it,its a "delonix regia" seed.(I have never made a soil for this plant before!)Please HELP!

Have you got a plant or only seeds? If you have seeds then a seed compost is fine, If it is a plant then any soil will do if it is just growing on.

It would help to know your whereabouts... What country are you in? Wait...now I see your avatar and says you live in Novi Sad. First question solved. Now, knowing how's your local climate would add up to the equation too... So, how's your weather?

I plan to keep it inside,I live in Eastern Europe,4 seasons..Thank you so much,I was not sure about planting seed in regular land...But its so obvious!In the beginning you grow a normal tree...Thank you so much again!

Also I would recommend you a careful reading of these two articles regarding the needs that must be covered if you want to keep your trees thriving. They are from this very own website:

1- www.bonsaiempire.com/basics/bonsai-care/bonsai-soil
2- www.bonsaiempire.com/blog/bonsai-soil-requirements

Of course, remember that these are general guidelines that should be met but they are not written in stone and you can bend these rules in order to adapt them to your local climate.

Alain