What is a difference between these 2 sentences I would swim when i was young and i could swim when i was young

The past tense of the word “will” is “would.” “Will” by itself is used for the future tense; it denotes the future possibility of somebody doing something or some event happening in the future. For instance, “I will go to the market in the evening today.” When we refer to a past incident, we use “would” in place of “will,” as in; “I remember my mother would take me to the market everyday when I was little.” The past tense of the word “can” is “could.” “Can” is used in the present tense and expresses the capacity to do something or the capability of someone to be able to do something. For example, “The parents and teachers of the girl know that she can excel in her class and can get admission to the best colleges.” When referring to the past tense, the same can be written as; “The parents and teachers of the girl knew that she could excel in her class and could get admission to the best colleges.”

In the first sentence, the speaker is describing his past when he used to swim. In the second sentence, the speaker is describing about his ability to swim when he was young.

I don't know