Drums on my track

[slinkymassive]

I am starting off, so most of this is new to me.

I have just bought a B1 mic, tascam u122 and cubase SX. I have been learning as I go along, and have managed to record a track. Basicly it is acoustic guitar and me singing.

Is there a way to add a drum beat after I have recorded, or should I lay one down first and play over it.

Secondly where can I sample a drum beat from, cubase has the facility, but i am not sure how I can actually put a drum beat onto a track. Is there additional software I need to buy? Can someone talk me through how to do this. I do not have a midi.

Thanks

Pete