When I copyright something what exactly is protected?
The specific interpretation of the design concept is protected. I know that is kind of a vague answer, but without seeing your design, it's impossible to give better info.
If your design features text (phrase, slogan, tagline, saying, word, etc), the text itself is not protected.
If someone changed the spelling or used the plural form of my saying would I be safe? i.e. If I copyrighted "Crazy Trend" could someone use "Crazy Trends"?
"Sayings" are not eligible for copyright. But they can be trademarked as long as they meet the other trademark requirements. Specifically, the mark needs to "identify the source of goods or services."
Generally speaking, changing the spelling or using the plural of an existing mark would not automatically be ok.
So if you owned the mark "Crazy Trend," you would have legal rights to prevent someone from using "Crazy Trends" because it is confusingly similar. Likewise, if someone else already owns the mark "Crazy Trend," they can prevent you from using "Crazy Trends."
But am not sure if the text is copyrighted.
No, it's not copyrighted.
So I went to the USPTO and did a trademark search and found that part of the word is trademarked. I would hope that my design wouldn't be infringing on their mark (or I would just change the text). Not really sure how to do a copyright search.
It really depends on the specific marks in question. It may be infringing or it may be perfectly ok. We would need more info to give a specific answer. If you don't want to reveal the info on the forum, feel free to PM me. Or better yet, you can consult an IP attorney.
I was getting confused with trademark and copyright.
Copyright is for works of art, such as t-shirt designs.
Trademarks are for brand names and logos.