To become a member of a team account you should first have a personal account. With a team account you have the option to add your company logo and primary color. The logo and color will replace the SignRequest branding during the entire signing process (from the emails sent till the placed signature).
In addition, you can invite team members to your team account. All documents sent from within the team account will be visible for all team members. Any documents sent from within your personal account are only visible for yourself. You can switch between your accounts by clicking in the main menu (upper-right corner).
While a team account is intended for multiple users you can also create a 'team' account for just one single user. In that case the main benefit is the ability to add your own logo and color.
Learn more on how to create a team account here.