Tell means to say something to someone. In this case tell something to someone is talking about giving advice, you want the person to hear it and apply the words you "tell" them.

Shucks is an older slang word when you don't know what to say. When you receive a compliment, people often say "Awe, shucks" Or "Shucks, I don't know". Donald Duck often says it. It is not as common now. It does not relate to sucks at all. I would says stinks is the less vulgar version of sucks.

A product costs an amount of money. A seller charges an amount of money. A person can charge someone money or be charged an amount of money by another person.

Ice cream is uncountable. You can't have many ice cream. You would say scoop of ice cream, bowl of ice cream, gallon of ice cream. If you need to specify how it is served (slice, piece, etc.) it is uncountable.

Future continuous is better with action verbs. Feeling is a stative verb. The first sentence is better because it uses the cause and effect conditional clearly. If you want to be set a time limit, you can say "If you take this medicine, you will feel better for (time) 2 hours." Or if you want to say the medicine won't fix everything, you can say "If you take this medicine, you will start to feel better". The start implies it will help a little but not cure it all.

You have done exceptionally well in this class! Keep it up! (or Keep up the good work!)