Use magit-ediff to resolve merge conflicts
Use magit-ediff or 'e' on an unmerged item to resolve merge conflicts with ediff. Magit will set up an ediff with three buffers A, B and C. A and B are the original (conflicting) files, and C is the conflicted merge.
Use 'n'/'p' to move to the next/previous conflict, use 'a'/'b' to choose which changes (those in a A or B) should be the ones to keep in the merged file.
You can always just switch to buffer C and edit what the merged version should look like.