"Told" is the past tense of "tell". "Said" is the past tense of "say". You use the verb tell when the information must be communicated to someone. You can’t just tell something, you have to tell something to someone. This is not true for the verb "say". Say can be used to express your opinion / when the receiver isn’t mentioned in the sentence / for exact quotes. Examples: I told him, "Take a sit". I said that he likes cats.

"Told" is used when there are necessarily two parties: a speaker and a listener. ✅"He told me", "you told your mother", "I tell you", etc. In the passive voice, the speaker might be just implicit, "I was told to do that (by someone)", "You were told to clean up this mess (by your girlfriend)". ⛔️Incorrect uses occur as in "I told a word", "You told many things last night", etc. when a listener is missing. "Said" is used when just the speaker is mentioned. ✅"You said many things last night", "Because she said so", "I say let's go!" In the passive voice, both speaker and listener can go implicit, "It has been said". ⛔️Incorrect uses occur when you mention both speaker and listener "I said you", "You said her to leave", etc. A same sentence can be written with either of the two: ✅You said we would stay together forever. ✅You told me we would stay together forever. ⛔️You said me we would stay together forever. ⛔️You told we would stay together forever, But notice the "told" version requires to introduce a listener ;)

The language models are: "say smth to smb" "tell smb" but there are expressions to remember too, such as: tell the truth, tell a lie, tell the future, tell time, etc.