The House of Representatives and Senate are the two chambers of Congress. They share legislative responsibilities, but their elections and institutional roles differ.
The House has 435 voting seats, all regularly contested every two years. The Senate has 100 seats, two for each state, with six-year terms staggered across election cycles. Source: USAGov.
District representation versus statewide representation
A House election takes place within a congressional district. A Senate election takes place statewide. That distinction affects which voters belong in a relevant poll and which results belong in a comparison.
A national headline about a state's politics can conceal substantial differences among its districts. A party could win a statewide race while losing several House races in the same state.
For practical ballot questions, your address identifies your House district. Your state identifies your Senate representation, although a Senate seat is not necessarily contested in every cycle.
Why the chambers behave differently
Both chambers must agree on the same legislative text before it can normally go to the president. The Senate also has distinctive responsibilities concerning nominations and treaties; the House has its own constitutional responsibilities, including the initiation of revenue bills and impeachment. Source: the Constitution's text.
Consequently, “winning Congress” is an imprecise phrase. Ask whether the claim refers to the House, the Senate, or both.
A simple example
Suppose a party wins a House majority and proposes changing a tax credit. That victory gives it an opportunity to shape the House agenda. It does not mean the Senate will accept the proposal or that the president will sign it.
Conversely, a party's Senate majority can matter for confirmation votes even when the House has no role in confirming that nominee.
Which race should you watch?
Follow your district for representation, the applicable statewide Senate contest for your state's seat, and the national chamber totals for control. Keep those layers separate.
A district poll cannot answer who will control the whole Senate. A Senate result cannot establish how every district in that state voted.
Related reading: Senate classes and majority thresholds.