It does give an indication of who'd win if the election were held right now, but it's only so reliable. Right up till the last minute in 2016 the polls had Hillary far ahead of Trump, but we know how that turned out. Still, that year was somewhat of an outlier and they're usually not that far off. Really it depends on the methodology of the individual poll, inherent biases, sample sizes, demographics, etc.

These things can also be deliberately manipulated by pollsters to give the results they want.