If you want to bridge your sub to 2 channels just say rear left and rear right for instance, you put the positives together and negatives together. So coming from the sub box you'll have a + and -, on the amp you'll have like + - and + - for each speaker, you put the sub negative to both the negatives on the amp and the sub positive to both positives on the amp. Easier done than said lol
But once you get the hang of it, its pretty simple. Also to add with the clarity of speakers, theres nothing better than having your speakers running through an amp, it comes down to the tune just like a car. If its not tuned properly it'll sound shit. If your cars not tuned properly it'll run shit lol