'Yo' is put on the end of a sentence when you want to emphasise something and you're assuming it's the first time that the listener has heard of it, or you are telling the listener about it for the first time. For example if, you were saying you think something is delicious, you could say 美味しいですよ "Oishii desu yo". You are putting emphasis on how delicious this food is, whilst assuming the listener didn't know you thought it was so delicious. As Georgeさん said, it has the meaning of something like "I tell you": "I tell you, this is delicious!".
If you wanted to put emphasis on a sentence whilst seeking agreement from the listener, then you would add 'Ne' to the end of the sentence. When using 'ne', you are assuming the listener already knows what you are telling them, but you are saying it to seek their agreement. For example, if you were saying something that both you and the listener were eating is delicious you could say 美味しいですね "Oishii desu ne". The 'ne' here acts sort of like "don't you think?" or "right?": "This is delicious, don't you think?"
Hope this helps! :)