Opening a small business

Any business in Germany needs to be registered at the Gewerbeamt (of the town where the company's main office is). So that should be your first port of call.
There are many different legal entities that a business can have, with vast consequences. If you are not familiar with those, it is advisable to engage a startup consultant to guide you.
In some professions, certain prerequisites are needed to run any business, e.g. diplomas, permits, health certificates, etc. The relevant trade association can help you understand these.
You also need to register your business with the tax authority and get a tax ID. Proper bookkeeping for tax purposes is complicated (and penalties stiff), so you probably need to engage an accountant and a tax consultant.
And, last not least, if you are not conversant in German at a near native level, it is basically impossible to manage everything well. So you will also need a translator in this case.
Good luck - yes, that is another requirement (on top of a good business plan).

thank you very much for the help!!   Do you know any consultants or companies that i can get in touch with to help me with the preparations? and one last queston- if my partner is not from europe ( i am from greece) ,he is from Iraq,how can i help him to join me ?

I don't know any startup consultants that I could recommend, but I am sure you can find them with Google.
As far as I heard, it is very difficult to get a visa for a non-EU citizen based on starting a business here. It is probably better you establich the business first and then hire him as employee.

Thank you very much  again for your help!!