Present tense:
* wissen: This is the most common word for "know" and is used when you know something as a fact.
* kennen: This means "to know" someone or something in a familiar way, like knowing a person or place.
Past tense:
* wusste: Past tense of "wissen"
* kannte: Past tense of "kennen"
Examples:
* Ich weiß, dass die Erde rund ist. (I know that the earth is round.)
* Ich kenne Berlin sehr gut. (I know Berlin very well.)
* Ich wusste es schon lange. (I knew it for a long time.)
* Er kannte seinen Weg. (He knew his way.)
It's important to choose the right word based on the context and the type of knowledge you want to express.