The ー is for a long vowel sound. As for the tsu at the end of sound effects, I asked someone once, it's supposed to kinda... cut the sound short...? I don't really know who to explain that....
The small tsu doubles the constant after it. For example: だって Or かっこう Or そっと Would be Datte, Kakkou, and Sotto respectively. Though I don't know if any of those are real words, I was just giving you an example.