This can be done in two ways from a person record:


On a person'position record, click the pencil icon against the person’s current role (1) or click the + icon to create a new role.   


OR using the candidate tab on the person record, click the Add position button.


On the company line, you have a choice of having a text value (if you dont need the company record on your system) or a company record.  

To set a company record, click in the field shown (2) and either search for or add a new company record.