Find Steed says that:
You summon a spirit that assumes the form of an unusually intelligent, strong, and loyal steed, creating a long‑lasting bond with it.
[...]
Additionally, if your steed has an Intelligence of 5 or less, its Intelligence becomes 6, and it gains the ability to understand one language of your choice that you speak.
Given that it's loyal, intelligent, and understands you, you can certainly command it. As for what it can actually do:
Appearing in an unoccupied space within range, the steed takes on a form that you choose: a warhorse, a pony, a camel, an elk, or a mastiff. (Your GM might allow other animals to be summoned as steeds.) The steed has the statistics of the chosen form, though it is a celestial, fey, or fiend (your choice) instead of its normal type.
So it can do anything that a creature of the type whose form it took can do. For example, if your steed takes the form of a warhorse, it has access to the warhorse's Hooves attack and Trampling Charge ability. Anything more than that is up to you to negotiate with your DM, although it would certainly be reasonable to expect it to, for example, pull a wagon.
Note: Jeremy Crawford, official source of rules interpretation for D&D 5e, agrees that the steed can attack independently.
Ryan Hagan: Following up on yesterday. So Find steed steed can attack on your turn? What about not mounted? Forums are abuzz.
Jeremy Crawford: While ridden, the steed follows the normal mounted combat rules (PH, 198). Unridden, it has normal action options.
