The U.S. Senate is the upper house in Congress and the U.S. House [of Representatives] is the lower house in Congress.
The senate is composed of two elected officials from each state, 100 total, regardless of population (This is where libs from California bitch that they have way less power than say those living in Wyoming). The senate is considered more prestigious as its members are elected to six years terms with 1/3 of the body elected every two years. It holds power over confirming the president's cabinet members, federal and supreme court judges, executive department leaders, ambassadors, and a handful of other things.
The house on the other hand plays a more legislative and financial role. It introduces bills that, with the approval of the senate and president, could eventually become laws; said bills can also affect government budgets, federal spending, taxes, and various other financially-related things. Its entire body is elected every two years. The house is proportional to a state's population, so more heavily populated states like California have a whopping 53 representatives versus only 1 representative for say Wyoming.
Ideally, the senate and the house are supposed to work together to draft, debate, amend, and approve legislation, budgets, spending bills, and many other things that ultimately go to the president's desk where he can either agree and sign it into law, or disagree and veto (kill) it. It is possible for both chambers in Congress (The senate and the house) to override a presidential veto with the help of a supermajority (Nearly all members have to agree to pass it) but this rarely happens; I think in all of Obama's 8 years as presidents, Congress only successfully passed veto'd legislation once.