Your reputation is a rough measurement of your influence within the community and how much the community trusts you. Whenever someone promotes content you have created or chooses to follow you, that indicates that they think you know what you are talking about. Whenever you introduce someone new to the network, that indicates a level of trust that person has in you to act upon your referral. These things will increase your reputation.
Your reputation is visible as part of your profile and will be associated with content that you create. As your reputation increases, your content will be more prominently featured.