There are several methods that can be used for melee training depending on your skills and chosen weapon.
The most common way especially as a higher level is training on a Modified Gnarlhound. To train here you will to have completed the Shadows of Yalahar quest. You must use an elemental weapon that does Fire, Energy, or Ice damage. You can summon a Mad Sheep every 12 hours using a Spellwand to train your shield as well. You may want to summon a sheep on a secondary character or ask someone else to summon one for you so you can train shielding efficiently.
If you are level 14 or lower you can use a weapon that is too high level for you and attack a Mad Sheep. The weapon must be at least the amount of levels higher than you as the attack on the weapon. For example, if the weapon had 50 attack you would need the weapon to be at least for level 64. A Mad Sheep can be summoned using a Spellwand. You can choose whichever location you want in Tibia and find another creature to attack you.
There are the old ways of training that don't work as well anymore since the damage rebalance depending on your character level. You can find either a creature that makes copies of itself that can be attacked or a creature that will heal itself and not do too much damage to you. Some examples are a Slime, Monk, or Gargoyle. You can find these in many places over Tibia.
You can also train on a Sea Serpent or a Hydra. The northern Sea Serpent spawn has some areas where you can trap Sea Serpents or Young Sea serpents on a diagonal so they cannot attack you. As for a Hydra, you can find one in the Port Hope jungle just to the south of the Asura Palace, here. You can lure this Hydra along the water and find several spots with bushes and trees that will only allow two creatures to attack you. You can then train on the Hydra and any other small jungle creature you come across.