I want to know what i should know about proteins in general so i can
detect one in a test tube with a Special assay(sandwich assay).

if you have an antibody to the protein you can use an elisa test.
Thats the best way to detect the presence of a protein in a complex
misture.  Another is to use mass spec but for this you will need to
know the sequence of the protein. Do you know anything about this
protein, I assume you know the fuinction at least?