You can use this any time after you have taught your students the past simple tense. You can use it at the beginning of nest lesson to review to past simple or as a filler. You can cut the worksheet into four parts to use it for four students. Students tick the correct sentences and change the incorrect ones. After that you can have them translate the sentences into their first language. And after that you can collect the original slips of paper and make them translate the sentences back to English.