In combat, the beast acts during your turn. It can move and use its reaction on its own, but the only action it takes is the Dodge action, unless you take a bonus action on your turn to command it to take another action. That action can be one in its stat block or some other action.
You can also sacrifice one of your attacks when you take the Attack action to command the beast to take the Attack action. If you are incapacitated, the beast can take any action of its choice, not just Dodge.
If the beast has died within the last hour, you can use your action to touch it and expend a spell slot of 1st level or higher. The beast returns to life after 1 minute with all its hit points restored.
Maul
Melee Weapon Attack: your spell attack modifier to hit, reach 5 ft., one target. Hit: 1d8 + 2 + PB slashing damage.
Charge
If the beast moves at least 20 feet straight toward a target and then hits it with a maul attack on the same turn, the target takes an extra 1d6 slashing damage. If the target is a creature, it must succeed on a Strength saving throw against your spell save DC or be knocked prone.
Primal Bond
You can add your proficiency bonus to any ability check or saving throw that the beast makes.