Adding a new test company

Hi, I have been assigned the task of improving the way our company works with SAP. I don't want to play with the live version of our company, is there any problem in creating a new company so that I can look into user defined fields, tables, addons, reports etc.. without affecting the live database? For example, if a post a purchase order on a test company, will this appear on the live database?

Regards,

Thomas.