New contacts can be added to the CRM in the CRM module -> Contacts submodule.
There, click on the + button which will open a popup where you can enter the information about the contact that you are about to add. A single contact can be added by clicking on "Add single contact".
If you want to select the Company from one of the existing organizations in your CRM module, click on the X button, and search for the organization you're looking for. Don't forget to click Save so that your new contact will be saved to the CRM.