Situationally fixed tense use

Hi. Please read the scenario that was made up and tell me which tense you would use if asked.

Fictitious scenario: A new guy joined our group. We usually play a game every Friday night. One rule among many is that if you raise your hand first and answer the question, then you will get a strawberry (strawberry-flavored?) candy. Now, I am going to tell him about the rule (or a result that will occur if a person does something right). Which tense is correct to you?

Hi. If raise you hand first and answer the question, you will get (or gets?) a strawberry candy. Do you understand?

Also, in the above scenario-telling narrative, would you use the present "join" in "A new guy joined our group" instead of "joined" in the sentence and change some tense that follow like this?

A new guy joins our group. We usually play a game every Friday night. One rule among many is that if you raise your hand first and answer the question, then you will get a strawberry (strawberry-flavored?) candy. Now, I have to tell him about the rule (or a result that will occur if a person does something right). Which tense is correct to you?

Thank you.