The documentation on the installation of cutadapt is just a bit 
misleading, as far as I'm concerned. Cutadapt was just installed as 
a Python package. The cutadapt executable is probably in 
/Users/yc/Library/Python/2.7/bin.

If that folder is already in your PATH you can just type cutadapt to 
run the program. Otherwise, you'll have to type the 
full path. /Users/yc/Library/Python/2.7/bin/cutadapt

As long as you're the only user using the program, it will work fine.