A logical fallacy is a "failed/flawed arguement". I've typed up a few common fallacies for you. See if you yourself display some of these fallacies and if not, keep them in mind so you can point out the flaws in your debating opponents argument.
It basically means attacking the person, and not the argument. Mere insults don't count as ad hominems, that's just being rude. An ad hominem attack is when you try to discredit an argument based on prejudice instead of reason and logic.
A: I think cake is better than pie.
B: Well, you're wrong because you're an idiot.
A straw man is when you construct your opponent's argument in a way that is easy for you to discredit. A good way to describe it is to imagine you make a man made out of straw and throw it in front of your opponent and burn it, you do this because it's easier to burn straw than human flesh. You say "that's your straw man", while your opponent is wondering what the hell is going on.
A: I think pie is better than cake
B: So, what you're saying is: Pie is the best food in the world and anyone who eats cake is an idiot.
A: ...? *continues munching pie*
No true scotsman
This is a way to distance yourself from the bad apples of your certain organisation or group. Try to imagine two scotsman. One is wearing a red tartan kilt, while the other wears a green tartan kilt. The red scotsman shouts "NAW TRRRUE SCOTSMAN WEARRRS GRRREEN!".
A: I think pie is the best thing in the world and anyone who thinks otherwise is gross.
B: I like pie too, but we all have different tastes buds, so no big deal if someone else doesn't like it.
C to B: A's not very nice, is he?
B to C: Well, he's not a true pie-eater, so don't listen to him.
Appeal to ignorance
Claiming something must be true because it hasn't been proven false. Not to be mistaken for the common religious/atheist argument of "we don't know if god is real, because it can't be proven true or false."
A: *Takes a bite out of space cake* Brah, do you think aliens are real?
B: *Swallows his bite* Dude, dude... think about it, no one has proven aliens to be non-existant, so they MUST be real. *mind blown*
Appeal to popularity
Claiming something must be true because a large portion of a population believe it to be true.
A: *Takes another bite* That's not really an argument..
B: *Drooling* Okay.. well.. quite a lot of people believe it to be true so that proves it.
A conclusion based on the presumed fact you are debating to be true.
A: What proof do you have that god exists?
B: Well, the bible says so.
This literally means "you too". or to put it in terms you understand "well, you do it, so why shouldn't I?"
A: Hey, dude you should stop eating so much cake.
B: Well, you eat too much pie, so why should I stop eating cake? *dies of a heart attack*
Those are just a few fallacies. There are a lot more, and I'll give you a link to look some up for yourself if you want. Make sure to keep these in mind when debating or arguing.