う・よう + とするTry to, Attempt to, To be about to

When combined with the auxiliary verb う (or よう), とする carries the meaning of 'to try to do (A)', or 'to be about to do (A)'. The case marking particle と in this expression highlights a 'result'.

To use おうとする, modify the (A) verb into its う or よう receiving form, and then add とする.

As う and よう mark volition (the express intent to do something), とする adds the nuance that the express intent has been decided, and all that remains is to 'do' the action. This translates quite closely to 'to endeavor to do' in English, where the past form 'endeavored to do' will suggest that the attempt was unsuccessful.

Caution

ようとする is also regularly used to indicate when one action interrupts another. In these cases, the nuance is not quite 'to have endeavored', but more '(A) was already underway, when (B)'. Again, it will just show that the (A) action was decided upon 100%, when something caused an unexpected change.