How can i show my dog to sit?

i have a 5 moths old yorkie i got him a month ago. i've been showing him to sit with a treat but when i do it without the treat he wont sit. i think he got the wrong message just like with the wee wee pads . when i got him wee wee pads i put him on them and he tought that it was a bed so he just lays down on them no matter wat i tell him!!