Microbiology as a science of studying Microorganism concentrate on studying these subjects; First of all four major fields are:

Bacteriology

Virology

Mycology

Immunology

And students usually study about these issue and subject in their Microbiology courses :

Taxonomy

Growth parameters/ Growth kinetics

Identification and characterization (microscopy, Gram’s staining, molecular identification, biochemical characterization)

Classification (prokaryotes, eukaryotes, archaea)

Mode of nutrition

Significance of microbes

Immune responses

Antigens and antibodies