I'm not too good with tab. Belive it or not I prefer to read dots.....

I need help with Black Dog. I can play the notes & solo etc but I cannot consistently nail the start each time the riff starts. the singing has no backing and it's here that dots & time signatures would be really useful.

Would someone please tell me such things as the time sig of Black Dog, How to nail the start of the riff each time and how in general do I infer timing from tab?

Thanks, RobSm (newbie)