Here is a link to a manual for a machine similar to yours.
http://www.sewusa.com/Sewing_Machine_Manuals/JC_Penney_Manuals/3400_Instruction_Manua.htm
The 1/2 button says "buttonhole lever". The "H/L" says "speed for two-speed motor".
The 3400 has cams but yours looks like the cams are built-in.