Who do they poll? They select a random sample from the population they are interested in finding out about. A representative sample for a nation the size of the US is a little over one thousand people. They usually select phone numbers at random, and then call and call until someone answers their questions. If too many people refuse to answer, the poll results are likely to be skewed.
You have to remember that they are polling people that represent millions of others. Your friends may all disagree with the poll, but the poll can still be right, Your poll of your friends is not a random sample. It’s called a “convenience” sample. Thus, you can not generalize from your poll and have anyone believe you are talking about anyone other than your friends.
I have been polled several times. The last time by an outfit in Canada that seemed to be looking at attitudes about politicians and the economy. I have no idea who their client was. It was not a push poll (where a candidate runs a “poll” that is really designed to “educate” people about the candidate and thereby encourage them to support the candidate). It seemed neutral.
Being liberal, I love to answer polls, because they do influence people. If my opinion is repeated by a few other people in the poll, then it may appear that the electorate is more liberal, which may encourage others to be more liberal. But, if the sample is properly selected, I won’t have that effect. Still, there’s always a chance.