To see what's in the clip tray, you can long press on a field (text message, email, IM chat, etc.) and select clip tray.
To delete items in the clip tray, long press on one of the items, an X should appear next to each one. Tap X to delete.
Depending on which keyboard you are using, if you are using the LG keyboard, you can long press the microphone looking icon and slide over to select the square icon with the paper clip on it.