Trade Offer: Buy, storage capacity reached

[Damocles_]

When following the trading tutorial, it tells me to select a trade offer to buy something.
But the trade offer menu only shows "storage capacity reached".

When landing on that station giving the offer, i can purchase it via trade offers. But its quicker to just purchase it manually.

What are trade offers? Just a hint? But why confirm it then, if I have to fly to the station anyway to do the purchase the product?
Cant those trade be done remotely, and I just pick up the wares later?

And why does the tutorial not state that I have to first dock at the station that I want to confirm the purchase order?

Or are trade offers just the menu to allow trading for ships that are not currently player-occupied...