Why was the Senate formed? Why was it formed the way it was formed?

The Senate was formed to appeal to the smaller states that were worried that the more populous states would end up controlling everything.

As the Congress is designed, the Senate is intended to be the wiser and more steady group.  There are only 100 members, and each member has to represent a whole state (and, as a result, a wide range of interests).  Also, Senators get to serve a 6 year term before they have to be re-elected.  So, they are free to look at the big picture.  Finally, only 1/3 of the Senate is campaigning for re-election every 2 years, so as a whole the Senate is stable.

The House, on the other hand, was designed to be close to the people.  There are 435 members, spread around the states according to population.  So, each member of the House represents a smaller area (except in states like Vermont where there is only one House member for the whole state).  Most important, House members have to be re-elected every two years, and the whole House is up for re-election at the same time.  So, the fact that they are basically always campaigning keeps them closer to the people.