To create a company head to Contacts > Company > New Company

Fill out the information in the fields provided and then click on Add Company:

To edit the details of an existing company, Go to the Company Tab and hit the 3 dots next to the Company and hit Edit Company, to delete a company click on Delete Company:

At the moment the only way to enter contacts into a Company is by manually heading into their Company tab, Searching for a company, and then adding them to it:
You can mark multiple contacts and then switch between them for ease of adding contacts to a company in bulk.