You work through your Representative. This requires patience, diligence, and a superhuman capacity to sink disappointment.
Occasionally though, you will see verbiage from one of your letters end up in a bill. So it does work.
Right now you have an electorate mostly equipped with near-instant communication and responsive to mass information campaigns, governed by a legislature that works at a snail's pace, lacking in adequate transparency, and with no direct linkage between the popular will and the legislative process; effectively a large complex machine which voters are given a limited right to kick every 2-4 years in hopes that this will rearrange the internals enough to make it functional. Individual congresses and executive branch administrations can be good or bad to varying degrees, but the system as a whole is simply not adequate for the governance of the society and economy that has grown up around it.
I laugh every time I think to myself that my vote can make a difference.
I believe democracy works because we can vote out a government we can see is working against our interest. I don’t think democracy is that important for voting in a party for its policies.
I certainly have never experienced that I can vote in a particular policy I believe in.
Occasionally I think I can vote against a party that is pushing a policy I don’t like, but often the policy comes to fruition anyway (maybe delayed until the next change of government).
And I live in a country with MMP where my vote makes more of a difference than a two party system.