ok, so i was creating a character in blender for my game but when i parented the mesh to the bones with automatic weights, i quickly found that when i moved bones on the left side of the body it affected the right side but the right side had no affect on the left. when i redid it the same thing happened so i applied the mirror modifier and did it again and it work perfectly but then when i was doing the weight painting the weight painting wouldnt affect both sides because i didnt have the mirror modifier. can anyone explain what could have happened if you can understand what i am trying to say? thanks.
I guess what you want is to create symmetric vertex groups so you don't have to repaint for the left what you've already painted for the right? Once you have finished the weight paint on a side, stay in Weight Paint mode, go to the Properties > Data menu, then click on the button on the right of the Vertex Groups list, choose Copy Vertex Group, a new vertex group is created, then click Mirror Vertex Group, the group has been mirrored. But this method only works on a real symmetric object.