It’s hard to know where to start. I will have to be vague Disease bad, Uses in industry good (production of proteins from E. coli such as insulin etc).

Firstly bacteria colonize our gastrointestinal tract which contains more than 400 different bacteria.
In science, bacteria like Escherichia coli or Bacillus subtilis are model organisms (with E. coli being the best studied organism in the world). Therefore E. coli has been extensively used for many experiments in molecular biology including the expression of foreign proteins and other molecules. And this leads us directly to industrial processes at a large scale like the production of insulin.
Furthermore, bacteria are used in the treatment of wastewater and bioremediation, because they can metabolize almost every substance.
Another important (yet problematic) application is the extraction of metals trapped in stone. A bacterium known as Thiobacillus ferrooxidans is responsible for this, but it produces a significant amount of sulfuric acid in return, which is harmful to the environment.
And there is the food industry. Products like yoghurt and cheese (along with sauerkraut, coffee, cocoa and butter – to name only a few), for instance, are the result of bacterial fermentation processes. Vinegar is produced by the bacterial fermentation of wine.

Bacteria are very small organisms, usually consisting of one cell, that lack chlorophyll (a green pigment found in plants that allows for the production of food). Bacteria are found everywhere, in the air, soil, water, and inside your body and on your skin. They tend to multiply very rapidly under favorable conditions, forming colonies of millions or even billions of organisms within a space as small as a drop of water.

Bacteria can also be bad, especially when it comes to diseases. It can be serious when you are immunocompromised, such as in the case of an infection by staph aureus.

Bacterium can colonize in other areas of the body besides the GI tract. The lungs, brain, and skin are a few other places. E. coli exist in the GI tract already and are not the same as those you would get from undercooked foods. As for Staph aureus, that is found during on human skin during the course of someone’s life. It is also colonized in the lungs of most healthcare workers. Bacteria can also form endospores when environmental conditions make it necessary for their survival. There is a ton of resources out there.

Bacteria are used in the chemical industry to make pharmaceuticals and agrichemicals. Since they grow easily and quickly, they can be used in molecular biology, genetics and biochemistry.
Our understanding of bacteria allows the biotechnology field to produce insulin, growth factors and antibodies for the medical industry.