how to create promotion

here are my senarios for which i need to create promotion . can someone please help me with this.

1. Buy one product A and get one product A free.

2. buy product A at a regular price and get 50% off any product B

( any product from the product line)

3. Buy one product at regular price and get second product 50 %

4. Buy any product of category A at a regular price and get any type

of B for 10

5. Buy any category of product line A and get a set of 4 product b

free.

6. get a A free with purchase of any B.

7. but product A is $4 or purchase 3 product A $1.99

8. get 20 % off on already discounted product.