It is recommended, but not necessary, to grease the stem, the seat post, and the pedal threads.
The purpose of greasing these parts is to keep them from seizing later on.
Any basic automotive grease will do the trick. You can find some at any auto supply store.
The chain should also be lubricated with a bicycle chain lubricant. These are available online, in bike shops, and often in big-box stores. Please do not use WD-40. WD-40 is a great anti-seize product, but it does not have the recommended lubricating properties.
This video might help:
Please help our co-pedalers by voting if this article is helpful or not.