Tax class ?

Hi all.
Could someone explain what tax class is or what i should put it down as ?
I got to fill this bit out on the V62 form as i didnt get the logbook off the previous owner and have no clue what to put.
Its for my directbikes 125cc if that helps and thanks in advance.

 

motorcycle, remember to do the SORN at the same time.

 

Thank you and why sorn ?

 

tax or sorn doesn't transfer to the new keeper. you are responsible for the tax status of the vehicle from the date of your ownership. DVLA will process both at the same time making you ok until they process the V5.

 

Oh yeah i forgot about that. Ill sorn it then tqx it once i get the new keepers v5