Connectioning a second pc on another level in my home

Go wireless to the second story.

hi
I think you will need one "Switch" (name of device - which is used to provide connections for more than 5 computers at a time)

So in the market there are variety of switches available like 5 port switch (for 5 computers) 8 port switch (for 8 computers) like wise.

So you need to purchase switch.

You can use alternate for switch is HUB (same as above)

So once you are done with that, let me know so that we can proceed further with configuration of you network (for 3 computers)