Applications can have a Company or Trust as the Primary Applicant. Company or Trust records are structured in the same way as People records, just with different fields on the details tab.
From the Company Section
Click the Companies in the main navigation menu.
Click a new tab to start a new Company record.
NOTE: your Company/Trust record won't be saved until you add some data in to it.
From an Opportunity
Open your Opportunity, select the Lead Capture tab and click +add Company under Contacts
A new tab will open where you can add their details
To add a Company or Trust you have already created to an Opportunity:
Open your Opportunity, select the Lead Capture tab and click Link Existing
A search window will display. Type the Company/Trust name, select in the list and hit save
NOTE: When using the Link Existing button in the Contacts section of an Opportunity record, the Company records will appear in the search along with the People records.