problem on Ranger Command

The test of Command says:
...On a hit, it does as you say and grants you the benefit of the Trick of your choice...

Does it mean that the companion do anything you command him to do and moreover he perform his trick, or that you can command only the trick and not any task?

Up the question, if someone could answer and I add

To have the companion perform the trick (e.g to get the +1 to follow a trail) you have to roll Command or they get the trick automatically?

i would say that in the narrative the animal companion does what you want them to, and that narrative action gives you the mechanical bonus of a trick of your choice. if you failed, your animal companion would disobey you in the narrative (or maybe just ask for belly rubs) and you would gain no bonus from your companions trick.
yes, you have to pass a roll to gain a benefit of a trick.

The rules could be better here, yeah. The bonus you choose should follow from the fiction in some way.

The animal companion follows your command to the best of its ability. The bonus mechanically reinforces that, the rest is up to the GM.

You say "I tell my dog to fly!" and the GM says "I just looks at you and cocks an ear."

You say "I tell my dog to tackle the orc shaman!" you make the roll, choose your trained for combat bonus, and the GM says "It grabs the shamans arm and drags on it. It's not enough to actually bring him down, but it does open him up to your attacks."