The procedure to appeal should be explained in the refusal notification. Basically, it seems you should complain in writing, explaining why you think you do qualify for a visa. There is a page about that (in German) on the website of the German Foreign Ministry but it's not very detailed.
You have not provided proof of sufficient means of subsistence, for the duration of the intended stay or for the return to the country of origin or residence, or for the transit to a third country into which you are certain to be admitted, or you are not in a position to acquire such means lawfully.
You should have a certain amount of money for each day you plan to spend in the Schengen area (even if you are staying with a friend) and also enough money to return to the UAE. You should therefore provide evidence of that (e.g. bank account statement). Having a return ticket would also satisfy the “return to the country of origin or residence”.
The information submitted regarding justification for the purpose and conditions of the intended stay was not reliable.
This one will be tougher to satisfy. It suggests the consular officer does not believe you are coming to Germany for a course and suspects you might try to stay illegally at the end of the stay. Perhaps they don't consider the school to be serious or do not believe your family friend can really host you. Did you submit some confirmation of your registration for the course?
It's a slightly different issue but showing you have reasons to come back to the UAE (say a school registration, a job, a house, a family) could also help alleviate concerns. Unfortunately, those decisions are sometimes a bit arbitrary and it's not always possible to do something about it.