To the untrained eye, the triceps dip may be confused with the chest dip. As their name indicates, the difference between the two is the muscle group they primary aim to target. The triceps dip is performed with the torso upright and arms tucked in close to the torso. By performing the dip in this way we are placing the majority of the load on the muscles responsible for the extension of the arm, i.e. the triceps.
If you do not have sufficient strength to perform the triceps dip using your own bodyweight you can instead use a chest dipping machine (either levered or assisted) to develop the necessary strength. Just remember to perform the dip using the form discussed on this profile to ensure you target the triceps and not the chest.
Once you can perform the triceps dip with your bodyweight it is recommended you invest in a dipping/chinning belt so you can add additional weight as you dip.