"Öyle bir bakıyorsun ki" can mean "You, looking like such"
Here "bir" is used as a "such", an adjective.
"Buraya bir otur" can mean "Sit here a little"
Here "bir" is used as "a little" and used as an adverb.
These examples use "bir" as different figure of speeches.
You can use some more examples below:
- Bana bir baksana => "a little"
- Olur da onu bir görürsen, selamımı ilet = > "if by any chance ..."
- Maalesef bir işim çıktı => "some" (used before an object)
So basically, the meaning of "bir" can change according to the context of the text and what verb its conjugated with.