Full-round actions take both your standard and your movement action to complete. However, you still get a bonus action when taking a full-round action.
To charge you must reasonably have at least 10’ of movement and a clean line of movement between you and your opponent without obstructions or difficult terrain of any sort. When charging, you may use up to double your movement to close and still get an attack. You make this attack at advantage, though until your next turn, your opponents get advantage on attacks against you.
As a full-round action, you can use a melee weapon to deliver a coup de grace to a helpless opponent but not a grappled one. You can also use a bow or crossbow, provided you are adjacent to the target.
You automatically hit and score a critical hit. A rogue also gets her extra sneak attack damage against a helpless opponent when delivering a coup de grace. You can’t deliver a coup de grace against a creature that is immune to critical hits.
If the defender survives the damage, he must make a Constitution save (DC = 10 + damage dealt) or die.
When you use a standard action to make an attack, you usually only get one attack. If you use a full-round action to make a full attack, you make your standard attack as usual, but you can also use as many extra attacks as you have available.
Full attacks are different depending on whether you are using man-made or natural weapons. When using weapons to make a full attack, your first attack is made normally, at your highest attack bonus. Any extra attacks you have are all made at a -5 penalty. Natural weapons (punches, kicks, claws, bites, tail slaps) function differently, and each attack is made at your full attack bonus. See Natural Attacks.
You cannot use full attack when grappling an opponent unless you have at least one hand free. When using a full attack, you generally can't perform both ranged and melee attacks, unless the creature has an ability that allows this. When using full attack, you still may use a bonus action.
You can gain extra attacks from a variety of means. Most character classes gain an extra attack with a weapon when their combat proficiency bonus reaches +6 and +11. Creatures with natural weapons (claws and teeth) naturally have extra attacks. Some magical spells can also give you extra attacks by making you faster, by causing you to grow fangs, or other enhancements. Some special abilities also grant extra attacks.