What does 'Je pense donc je suis' mean?

The sentence 'Je pense donc je suis' means I think therefore I am. In the Word-by-Word translation, the personal pronoun 'je' means 'I'. The verb 'pense' means '[I] am thinking, do think, think'. The conjunction 'donc' means 'therefore'. The verb 'suis' means '[I] am'.