1. yes, i guess you can say that "repression" is basically suppressing the memories that you don't want into the unconscious.

2. Yes, you do have to memorize all the percentages of the normal curve. No need to memorize the decimal points though.

3. Archetypes are basically formed BECAUSE OF experiences, and these experiences are shared by all people. So it's trying to say that once upon a time, primitive people had an encounter with snake, and possibly it was a negative one. The thing is this wasn't the case for just a certain group of people in one region. It was the same for all. Whoever had encounters with snakes, the result was pretty much the same: getting bitten, feeling ill, dying, etc.

This common, widespread experience was SHARED by all people long time ago, and as their descendants and the descendants' descendants live, even if they don't encounter the same experiene, they will still have the same concept of snake as "evil" because according to Jung, this COLLECTIVE EXPERIENCE from a long time ago is basically inherited by the descendants, but goes into our unconscious. So even if we, of this generation, have never had an encounter with snakes, we still consider it evil. Not because we have learned of, or about snakes, but because unconsciously, we share the experiences of our ancestors, but since it's in our unconscious, we don't know that.

P.S: the snake example is just an example, not trying to say that that really happened. Also, the concept of collective unconscious itself is just a theory, not a fact. Just in case you are confused lol.