Get my bearings straight, get one's bearings, and find one's bearings are variations of one another. The phrases mean figure out one's position or situation relative to one's surroundings.
There is also losing one's bearings, as in no longer knowing one's relative position. Bearings used in phrases like these dates back to the 1600's.
Get my bearings straight, is an idiom. Idioms are phrases with words that when used together do not mean what they do according to dictionary definitions when used separately.
The Cambridge Dictionary of American Idioms defines the meaning of over 5,000 idiomatic phrases found in contemporary American English. Check out some of them at Idioms.thefreedictionary.com.