Hello...im new to the sport just discovered it last yeah and all it took was a couple 3.5lbs to 4lbs LMbass and im hooked  

Im still learning some techniques to be effective in the water...can someone tell me the reason/purpose of leader lines? why cant i just tie a lure to my main line? Is there any advantages or disadvantage of this kind of technique? does it really affect presentation? Please help.

i dont use leaders except on my c rig but   say your reel  has  braid on it  and you need a low vis line cause the fish are spooked by it use a leader of mono or fluracarbon   without having to respool your reel       and say your reel has eight pound test    but you wanna throw into a area with trees weeds  and some nasty looking cover youll need a strong leader of 20 pound test or so to horse that fish outta there  

i c thanks.

I agree with Cajun ,the c-rig is all I use a leader for.   I use flourocarbon P-line which has helped me considerably.