What is the difference between the pretérito indefinido and the pretérito imperfecto?

Using the examples of "Fui a la playa" for the pretérito indefinido and "Iba a la playa" for the pretérito imperfecto, we can translate both as "I went to the beach". However, the pretérito indefinido is used to talk about a completed action in the past that happened at a specific time; while the pretérito imperfecto is used to talk about a routine or habit in the past that does not happen now. For example, with the pretérito indefinido we can use specific adverbs of time, e.g. "anoche"(last night), "hace dos años" (two years ago), "en 2019" (in 2019) to explain when the action occurred. So, "Fui a la playa anoche" (I went to the beach last night) explains a completed action and when it happened.Moving to the pretérito imperfecto, it is not possible to use these adverbs of time, because the action did not occur at one specific time, but is rather occurred multiple times as part of a routine or habit. A possible English translation is "used to". In the same way that we cannot say "I used to go to the beach last night", we also cannot say "Iba a la playa anoche". Instead, we will use expressions such as "todos los veranos" (every summer), "cuando era niño" (when I was a child), "cuando tenía 9 años" (when I was 9 years old) to talk about past events or activities that occurred as part of a routine or habit. So, "Iba a la playa todos los veranos" (I went/I used to go to the beach every summer" explains an action that occurred routinely and not just at one specific point in time.