When combined with the 助動詞（じょどうし） (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 格助詞（かくじょし） (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.
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この子（こ）はなんでも食（た）べようとするから、お菓子（かし）は隠（かく）してね。
This one will try to eat anything, so please hide any snacks.
先生（せんせい）が話（はな）している間（あいだ）に帰（かえ）ろうとすると、先生（せんせい）に怒（おこ）られる。
If you try to go home while the teacher is talking, he will yell at you.
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.
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今年（ことし）は毎日（まいにち）日本語（にほんご）の勉強（べんきょう）をしようとしたが、時間（じかん）がなくて出来（でき）なかった。
I tried to study Japanese everyday this year, but I couldn't because I didn't have time.
クラスメイトのスズキさんに話（はな）しを掛（か）けようとしたけど、緊張（きんちょう）し過（す）ぎて話（はな）せなかった。
I tried to talk to my classmate, Suzuki-san, but I got so nervous that I couldn't.
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.
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家（いえ）を出（で）ようとしたら、急（きゅう）に雨（あめ）が降（ふ）り始（はじ）めた。
It suddenly started to rain when I was about to leave the house.
部屋（へや）が暗（くら）かったから電気（でんき）を点（つ）けようとしたら、妻（つま）に電気（でんき）を点（つ）けるなと言（い）われた。
As I tried to turn on the lights in my room because it was dark, my wife told me not to.