This phrase is often used to express that the speaker is aware that the other person possesses something, either physically or metaphorically.
Here are some examples:
* "Yo sé que tienes un coche nuevo." (I know you have a new car.)
* "Yo sé que tienes talento para la música." (I know you have talent for music.)
* "Yo sé que tienes miedo." (I know you are afraid.)
Remember that the specific meaning will depend on the context of the conversation.