When do you use "ты" verses "вы" ? They both translate as "you". Is one used as formal? Does it depend on the other endings in the sentence or who you are addressing?

When put together, they translate "you're" (ты вы or even вы ты)...is that right? Does is not matter which one comes first?

I have a hard time pronouncing " что". Keeping the "ч" and the "т" together without an "ы" sneaking in between has been really tough and I don't notice it like my Russian friends do...which makes it harder for me to correct it. One told me that I can pronounce it with a "sh" sound instead of a "ch" sound, but when I look up "што"...it is the word "into". Now, on one of the sites I found for pronunciation, the question "Что это" was pronounced with the "sh" sound...can you help me sort this out? Should it be "sh-to" or "ch-to"??