first thing is, to advice u we need to know about your work.
do your home work first. if u had done it then show it in the message only then we can provide u with necessary suggestions.

secondly,
functional block diagram (FBD) is a representation of logical flow of the process in the form of blocks. the main advantage of functional block diagram is that it can show parallel execution of more processes. it is one of the five programming languages used for PLC programming which are defined by IEC61131_3.
where as a more popular flow chart is a diagrammatic representation of the program or process.

both are graphical languages, and both use special symbols.
for representing complex processes it is better to use functional block diagram FBD.

for more information u can search google.