What sentences are correct?
She danced beautifully or she danced beautiful?
When I tidied up my attic,I found a bunch of yellowed letters /or/ when I have tidied up my attic,I found a bunch of yellowed letters.
They talked very clearly (or clear), so we could hear every word.
I knew I was late (or lately) so I started driving very fast (fastly).
She danced beautifully (or beautiful),so she had to win the contest.
I've never told (or talk) to him personally.
May I introduce you to Mr. Jones?// May I introduce Mr. Jones?

Is the text correct?
A pre-pay card is a kind of bank cards that allowes the owner spend only money he or she put on the card. They might be attractive because there are people who want to control their spending or don't give details of the bank card over the internet. Everyone who has a pre-pay card can use it on the internet and at most retailers that take Mastercard and Visa.

Question

What sentences are correct?
She danced beautifully or she danced beautiful?
When I tidied up my attic,I found a bunch of yellowed letters /or/ when I have tidied up my attic,I found a bunch of yellowed letters.
They talked very clearly (or clear), so we could hear every word.
I knew I was late (or lately) so I started driving very fast (fastly).
She danced beautifully (or beautiful),so she had to win the contest.
 I've never told (or talk) to him personally.
May I introduce you to Mr. Jones?// May I introduce Mr. Jones?

Is the text correct?
A pre-pay card is a kind of bank cards that allowes the owner spend only money he or she put on the card. They might be attractive because there are people who want to control their spending or don't give details of the bank card over the internet. Everyone who has a pre-pay card can use it on the internet and at most retailers that take Mastercard and Visa.

Answer

Correct sentences:
She danced beautifully.
When I tidied up my attic, I found a bunch of yellowed letters.
They talked very clearly, so we could hear every word.
I knew I was late, so I started driving very fast.
She danced beautifully, so she won the contest.
Personally, I've never talked to him.
May I introduce you to Mr. Jones?

A pre-paid card is a kind of bank card that allows the owner spend only money he or she has put on the card. They might be attractive because there are people who want to control their spending or don't like give the details of his or her bank card over the internet. Everyone who has a pre-paid card can use it on the internet and at most retailers that take Mastercard and Visa.

Answer

You've asked a number of questions, so I'll ask some in return. :)

1) Does "beautiful(ly)" refer to the verb or not? That will give you the answer.
2) Which verb form refers to the past, and which one refers to the present?
3) Same question as 1).
4) In English, can adverbs describe "to be"? Why/why not? For the second part, which one of those words does not exist?
5) Same question as 1).
6) What's the difference between "talk" and "tell"? What are the past participle forms?
7) How does the meaning change by removing "to you"? Is it incorrect?

The text needs to be posted under Notebook. Fortunately, there are only a couple of errors.