I've received) the sentence is in the present perfect. and it is used when you talk about something happened in the past but it is not determined when happened and it is used when you use these adverbs: never, yet,just, already Ex: i have never received a letter The second one is in the simple past it is used to talk about some thing in the past but you say exactily when it happened and this tence take these adverb: yesterday, lastweek, ago, last year Ex: yesterday i received a letter