The yellow parts are called the "variable regions", these are the parts that will differ in all antibodies depending on what pathogen they are up against. The variable region is a chain of different amino acids that are complimentary to the antigen on a pathogen. The rest is called the constant region, which is just made of up of polypeptide chains.
An antibody can help the body with two main mechanisms: Agglutination, and Neutralisation.
Agglutination is basically where a load of antibodies attach to pathogens and group them up into a clump of antigens, this makes it easier for phagocytes to engluf and destroy!
Antibodies will also neutralise a pathogens toxins that it produces, and if the antigen binds to a region of the pathogen necessary for "pathogenicity" it will neutralise the pathogen (basically destroying it).
Antibodies do not influence memory or anything like that.
3) You don't really need to know about this, they will never ask you a question about that. All you need to know is when a lymphocyte comes across a pathogen and binds to its antigen, it will go through a clonal selection phase where it select what it wants to divide into, it produces the correct lymphocytes for that pathogen. Then clonal expansion occurs where the lymphocytes divide by mitosis into T-killer cells, T-helper cells. Later on these cells may divide into memory cells.
4) Macrophages do come from the bone marrow also, they survive a lot longer than neutrophils which are the other types of phagocytic white blood cells, and when they enter the blood they are called "monocytes".
(Just to make sure you know)
The only white blood cells that engulf pathogens are phagocytes. These are macrophages and neutrophils, they perform phagocytosis on the pathogen. Lymphocytes do not perform phagocytosis, T-killers will inject H2O2 into a pathogen, or plasma cells will produce antibodies. T-Helpers produces chemicals called cytokines that stimulate B-lymphocytes and phagocytes to get into action and start killing some pathogens.
Hope I've helped a little! (Also doing AS biology)