Each node in a BHAV is numbered. This helps to identify a failing node in a log file and additionally allows easy linkage from one node to another. Linkage is done dependant on whether the OpCode just executed returned True or False. You have to link the node to either another node by number, or return True, False or Error.
You may find that BHAVs that you clone look a little messy in the linkage department. Clicking on the "Sort" button can often make things read a little clearer, although I often go through manually as it gives the opportunity to learn what the BHAV is actually doing.