That's ok, we're here to help! And you will get the hang of things steadily as you use the software 🙂
Let's tackle the lines where two walls connect. That happens somewhat commonly when curved walls contact each other. Since neither Join Geometry nor Wall Joins worked, I'm thinking like the other people said, using the Linework tool will be your best bet. This is on the Modify tab of the ribbon at the top of the screen, as shown here:
The tool designated by the red arrow and circle is Linework
In the drop-down menu which appears after you activate the tool, select <Invisible Lines>, then click the lines where the curved walls connect. They may still partially show in the 3D view; sometimes by scrolling in and out, you will see that the lines are not truly visible (they will likely disappear when you zoom in far enough), but the "dashed" look is just part of the software--the lines will not print when changed to Invisible Lines.
As for where the Floors contact each other, use the Join Geometry tool. This should make the lines vanish. If they don't, something is keeping the lines from vanishing which we could figure out if you post the .rvt file.