In Facebook, go to your HOME page, at the left side of the screen, find your list of group (if any) then find the group your planning to add your friends. Click to open it.
At the group page, at the upper right side of the screen under the MEMBERS list, there is a box + ADD PEOPLE TO GROUP.
Just type the name of the person you want to add, typing the letters of the person's name will open a drop down list of your friends, just click the name of the person you want to add.
