For this example I'll assume you want to copy files from the directory C:here to the directory C:there
Just replace the example paths with your real ones.

Copy only files not subdirectories

xcopy C:here C:there

Copy only files and all subdirectories (and their contents) xcopy C:here C:there /s /e

If you are copying over a network add /z

If some of the files already exist in C:there and you don't want to have to confirm overwrite for each one add /y

If you want to check what files will get copied add /l

and remove when your sure that you have the correct values.

The other two most useful options are /m

and /d:date

Check the help for an explaination of the last two.