The key to your question lies in the duration of that action, even in the past.
All of the actions you've mentioned terminate in the telling (that is they took place, and have now finished by the time you're reporting it).
I went to the beach.
I ate an apple.
We won several medals.
No one would ever confuse these items as things that were ongoing in the past for a time period. You weren't continuously going to the beach, eating an apple, or winning the medals.
By comparison consider the following sentences:
I was at the beach.
I was eating an apple.
I was competing, hoping to win several medals.
Notice how each of these examples don't seem to have an end point that is readily apparent? You were at the beach, eating an apple, competing. Essentially all of these actions took place in the past, but they were ongoing at this point in your telling.
These are examples of the imperfect tense to the degree that English has one. Unlike most other languages, English doesn't have quite such hard and fast rules regarding conjugation and tense.
So, when do you use the simple past vs the imperfect? An easy (but not unbreakable) rule is this:
If you're describing an action that was already done at the time of telling, use the simple past.
If you're describing and action that was ongoing when your telling takes place, then use the imperfect. This is especially true when you're trying to indicate an action was ongoing while performing another action:
I was at the beach and I ate an apple.
Note the mix of the imperfect and simple past here. The apple was eaten (finite action) while I was sitting at the beach (ongoing in the past).
Habits are tricky.
I ran five miles per day.
This can be either tense and you need context to decipher it.
I ran five miles per day (while I was on vacation).
I ran five miles per day (back when I was young).
Probably the imperfect, though you could make a case for this being the simple past.