trans and cis attachments to cyclic carbon structures

[Emi Nakahara 3F]

I am confused on how you are able to tell whether a substituent is attached trans or cis to a cyclic carbon structure. In the Introduction to Organic Chemistry textbook page 60, there is an example molecule of cinnamaldehyde, and its IUPAC name includes E because the aldehyde is attached trans to carbon three on the benzene ring. But I'm not really sure what that means or how to visualize it on the molecule?

[Sophia Rawson 1C]

I found this a little confusing as well, but understood it more after I thought of the benzene ring as a substituent. This benzene ring substituent is trans to carbon three, where O is attached to the double bond.