My experience with my ender is that if prints arent sticking to the bed. First clean it very well then some purple elmers glue stick.
If the part dont stick then your bed leveling and nozzle distance is in correct.
There is a file on thingverese for the ender that prints a spiral around the whole bed for leveling purpose.
Get it close by adjusting with say a index card or thick paper. Then fine tune the knobs while it prints. Always remember looten to raise the bed and tighten to lower. If its coming out thick and not smashed its to low. If it wont come out at all or barely its to high.
You want a coplue millimeter line wide that is maybe a millimeter thick.

Hope some of that helps
RobertR728