when do you put a comma at the end of the dialogue? and now a period? ex. "Sally and I are going to the park_" so do I put a period or a comma?

depends, but comma

Explanation:

I think of commas as small pauses, in this case id put a comma in the sentence. this sentence should be tagged with "said " after so it would go:

"sally and i are going to the park," said john.

If it were before: john says, "sally and i are going to the park." i guess. hope this helps a bit