If you want practical examples of what they do, go to digikey.com, search for the company names and click randomly on one of the thousands of hits.
Here's a microcontroller: https://www.digikey.com/product-detail/en/maxim-integrated/M...
Here's an I2C temperature sensor: https://www.digikey.com/product-detail/en/maxim-integrated/M...
Here's an RF amplifier: https://www.digikey.com/product-detail/en/maxim-integrated/M...
Here's a 3v3 DC-DC: https://www.digikey.com/product-detail/en/linear-technology-...