There are many subtle differences between the types of articulation that players use. In the clips below John Jenkins describes various tuba articulations.
The central technique for tuba articulation is called 'tonguing' and it means using the tongue to control how notes start and finish. As the player blows, the tip of the tongue touches the roof of the mouth just behind the front teeth. This is done by a quick movement a little like saying the letter 't'. The tongue briefly disrupts the flow of air into the instrument creating a slight separation between the notes...