Ignoring bad behaviour. Does this mean that when your dog pee's against the sofa you ingnore it, hoping it will not happen again? (for example) Or jumps on the sofa uninvited. DOes just ignoring the dog mean it won't do it again?

When working on troublesome behaviour, you need to understand what's reinforcing to a dog. So, the most common problem that is advised to ignore is probably dogs jumping up. Why do we ignore? Because the dog wants our attention, which is reinforcing; thus, relinquishing our attention is punishment for jumping up.

Peeing is self-reinforcing, thus ignoring (taking our attention away) has nothing to do with managing the behaviour. More training is needed, teaching a more desirable behaviour.