Hi, I know that the corners arent spaces, but is there any way to use the ability, either by moving over the space or do you just use the ability whenever you want.

The corners are spaces, and you have to end your Movement on the corner space to use its ability.

Note: if a threat card is moved to a corner space, you must encounter the threat card instead.

The corner spaces are spaces. They just do not have threat icons, therefore you do not encounter threats card, unless, as zealot12 has pointed out, a threat cards is on the space.

For example, the Cannoness can draw 1 card from any threat deck and place it on her space at the start of her engagement phase. If you are on a corner space, you could decide to draw from any deck instead of resolving the corner square ability.

As far as the ability of the corner spaces is concerned, you can only resolve those text boxes when you have successfully landed on the corner square. You cannot have these text boxes resolve any other ways. You must be on it to "activate" them.

If you are finding it too hard to land on particular squares, for example the battlefleet Antias is a good square to land on early on to gear up your character, I suggest you roll 2D6 for your movement and choose 1 of these die as your movement roll as a house rule. This gives you a bit more flexibility to land on particular squares that you want.