So I know that its supposed to connect to the WAN port on the router but unsure what the WAN port on the router is supposed to connect to on the modem.

There is one black port and 4 yellows (can’t post pic).

I used to have it in the black port but then one random day the internet stopped. So I moved it to one of the yellows and it started working again.

Now I have to keep it in one of the yellows. Is this correct? Also does it matter which yellow?

I sound like a dumbass just typing this out but this is the best way I can describe it.

EDIT link to photo: https://ibb.co/gdhq3fr