This is just to show you a syringe type tube of solder flux paste and what you can expect to get if you buy a syringe type tube of solder flux.
Using flux when soldering can
a) Help chemically clean electronic parts.
b) Transfer heat and help the solder flow.
c) Make soldering easier.
Extra flux can even be helpful with Multicore Solder which has in built flux.
Remember there are different typed of solder that may require different types of solder flux.
Clean excess old flux off after parts are cooled.
Electronics, Electronic components and Electronics Circuits. http://www.acomputerportal.com/electronics.html