The past tense of the verb ‘see’ is ‘saw’.
To understand why ‘saw’ is the past tense of ‘see’, it’s helpful to know a bit about irregular verbs in English. Unlike regular verbs that typically take on the ‘-ed’ ending to indicate the past tense (like ‘walk’ becoming ‘walked’), irregular verbs change their form entirely in the past tense. ‘See’ is one of those irregular verbs. In sentences, you would use ‘saw’ to describe an action that has already happened, for example: ‘Yesterday, I saw a beautiful sunset.’