Bigbys spell clarification

[dnd2016]

What it it saying? Is it just 5 feet? Can you cast on an enemy farther than 5ft? ...What if the enemy is 20 feet away?....Interposing Hand: The hand places itself between you and a creature of your choice until you give it a different command. It moves to stay between you and the target, providing you with half cover. The target can't move through the hand if its Strength is less than or equal to the hand's. If its score is higher than the hand's, the target can move toward you through the hand, but the space is difficult terrain

[Callak_Remier]

The hand is Large which fills a 10 by 10 feet square

[dnd2016]

Oh, because its a large hand, but can i still cast it out 60 ft on an enemy?

[Asmotherion]

It really says "Bigbi used to be a really Great Mage back in 3.5, but now look how the mighty have fallen".

Now, jokes aside:

It has a Range of 120 feet. That's how far away from you you can create the hand the moment you cast the spell.

It's Large, made of force, but does not occupy it's space (think of a giant ghost hand)

From this point on treat it as a creature.
It has a 5 foot reach.
It moves with a speed of 60 feet. (on your command, during your bonus action).

It then takes one of it's special actions described in the spell. (Still during your bonus action, still only at your command).

One is an "attack" option, one is a grapple and move option, one is a maneuver option were it provides total cover to you, and finally a grapple and attack option.

You can also think of it as a Combat Applicable Mage Hand/Unvisible Servant.

The bad news is, it's most useful ability most of the time will be the Interposing Hand, since without it you will probably loose concentration on the spell.