OP, I would look up Duverger's law if I were you. We are in a two-party system. One of the consequences is that we have two catchall parties. The parties are really just placeholders for the left and right. Our system does not really facilitate parties having specific platforms and sticking to them. They both try and get as many people is they can with whatever message they can. I'm sure if we read the two official platforms we would not really know what they were different on.
That does not mean they are not different. If you want to know the difference between Republicans and Democrats, take specific issues. On most issues, they differ. A classic example is abortion rights. Republicans are against them. Democrats are for them.
Things have changed recently however. Republicans used to be for small government for example, but in past presidencies they really have not stood by this.