Brackets are used for many things.
Two common ways i know it's of use are:
1) Two separate information .
e.g. 3+4-6+5
$${\mathtt{3}}{\mathtt{\,\small\textbf+\,}}{\mathtt{4}}{\mathtt{\,-\,}}{\mathtt{6}}{\mathtt{\,\small\textbf+\,}}{\mathtt{5}} = {\mathtt{6}}$$
But if you want 7-11
Expanded can be (3+4)-(6+5)
The information is separated so that you/and the calculator doesn't get confused.
$$\left({\mathtt{3}}{\mathtt{\,\small\textbf+\,}}{\mathtt{4}}\right){\mathtt{\,-\,}}\left({\mathtt{6}}{\mathtt{\,\small\textbf+\,}}{\mathtt{5}}\right) = -{\mathtt{4}}$$
2) Another way is mainly used in algebra for multiplying.
E.g. 3(x+4)
This also means (3*x) + (3*4) --> See how i used the first way of brackets there.
So i just showed you it expanded.
It = 3x + 12.
Also brackets is used in English for extra information (in scripts too) in writing. <---- I used it there.