So, instead of speaking with everyone in the state, senators rely on (or depend on or use) opinion polls (or surveys or questionnaires) that show what most people in their state think about important topics.
This is an easy way for a senator to know what most people think about a certain law without having to call everyone to ask.
Senators also try to create opportunities for interested voters to speak with them about pressing issues (or topics that they think are most important).
Voters can always call, email, or write to their senators to share their opinions.
Senators also have offices where they can meet with their constituents (or the people they represent).
They normally have an office in Washington, D.C. where the Senate sessions are held (or where they happen), and at least one office in their state, usually in the most important city or cities.
When Senate is in session (or having meetings), the senators are in Washington, D.C.
The rest of the time, they are normally in their home states, speaking with voters and planning what they want to do the next time the Senate is in session.