Help with my paypal money...?

I am selling to items on gumtree and have recieved an email from paypal saying that I have been paid 200 and to get it I have to send the item off and then send them the reference num (what is that and where do i get it?) and then they will check that im realy sending what the person paid for and then the money will be added..but i dont no do they mean it will be added to my paypal or where? and do i just send the item to the adress the person wnats it sent to or do i have to send it to paypal or what? please help!!!