What you want is:
cp -R t1/. t2/
The dot at the end tells it to copy the contents of the current directory, not the directory itself. This method also includes hidden files and folders.
cp dir1/* dir2
Or if you have directories inside dir1 that you'd want to copy as well
cp -r dir1/* dir2
If you want to copy something from one directory into the current directory, do this:
cp dir1/* .
This assumes you're not trying to copy hidden files.