What was the main objective of the Berlin Conference?

In late 1884, Otto von Bismarck, the imperial chancellor, and architect of the German Empire convened a meeting between representatives of fourteen European States to negotiate geographical fragmentation of Africa for their patrons. The Berlin Conference, as the meeting came to be called, offered European powers the opportunity to lay claim on parts of Africa's vast continent rich with minerals and markets. While European powers had explored Africa for decades prior to the conference, the objective of the conference was to cement the spheres of influence for the European powers amidst growing competition.
 
European powers had conducted exploration of various parts of Africa and an insatiable need for resources such as silver, gold, and bronze among others, and a demand for more market fueled intense competition among these states. As a consequence, there arose a need for each European power to carve out part of Africa and exercise their influence. This desire was the motivation behind Otto von Bismarck's call for the conference because he wanted to safeguard the interest of Germany as well as play European interest against each other. Berlin Conference objective of expanding European spheres of influence over Africa was achieved after three months of negotiations. Among the major players, the French curved West Africa for themselves, Belgians acquired the vast Congo and the British took control of East and Southern Africa while Germany took control over four colonies and Portugal two colonies in Southern Africa and one colony in West Africa.
 
Further reading
de Blij, H. J., & Muller, P. O. (2003). Geography: Realms, regions, and concepts (11th ed., pp. 298-300). Hoboken, NJ: Wiley.

The main objective of the Berlin Conference (1884-85) was to codify and legalize the European colonization of Africa. For a number of years, the European powers had been involved in what became known as "The Scramble for Africa." As the name suggests, the process of European colonialism had developed in a somewhat improvised, haphazard fashion, without much in the way of planning or foresight. One serious consequence of this approach was that the colonial powers often became bogged down in petty disputes with each other over territory. There was a real danger that these skirmishes could flare up into out-and-out war.
It was therefore thought necessary by Bismarck, who convened the Berlin Conference, to establish European colonies in Africa on a more formal legal and diplomatic basis. That way any territorial disputes could, it was thought, be amicably resolved, without resorting to conflict. However, Bismarck's motives weren't completely disinterested. Germany was a relative latecomer to European colonization and was becoming increasingly aggressive and expansionist. But as German territory in Africa was still dwarfed by that belonging to Britain and France, Bismarck wanted to make sure that German gains would be protected from potential incursion by the other European powers.
https://www.oxfordreference.com/view/10.1093/acref/9780195337709.001.0001/acref-9780195337709-e-0467