I am doing a layout of my house but I have a repeated glitch. When I pull the walls up,there are extra lines sometimes. Most of them I can erase with no ill effects. Sometimes doing so erases a face. I do not know why this happens or how to fix it.
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From what you describe, you most likely drew something wrong.
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That’s because every face has to be bounded by coplanar edges. They are needed to support the face, so deleting one means that you also loose the face. This is how SketchUp works.
To fix this you have to make sure that everything is coplanar (flat).
If you deleted a line and kept the surface around it it means you healed the two surfaces into one. That makes the lines surrrounding the face contiguous.
if you deleted a line on a surface and the faces around it also got deleted it means the two surfaces on either side had an angle towards each other so that they could never merge into one surface.
If the angle is really small it’s hard to tell that the line you are deleting is actually a corner in your geometry.
SketchUp requires total conformity to presise modeling in terms of planes being parallell in order for things to work
Sometimes you can have really small divergences from a clean geometry. If you try to use lines imported from cad for instance. Those pesky imperfections will ruin your modeling. The irony here is that SketchUp also throws bad geometry out in their own dwg export. So if you try do model from dwg geometry reimported into SketchUp nothing will work 
Other ways to get bad geomery: if you have small finer detailing in your model but also objects really far away in that same model, the accuracy go down, and can make it so that faces don’t form. That’s just the effect of that sketchup cannot store infinite desimals for a given number, just like any cad software. And if you have some geometry a mile away that will force the software to store those finer details with lots of zeros in front of their location points, and the accuracy will go down, because you have used up desimal places to store your geometry’s location in the floating point number system.
One way to check for proper geometry is to use color by axis. Your lines will light up in the same color as the axis system if they are actually parallel. This system will catch most imperfections
But not all, color by axis has a small margin of error which can lead you to believe a line is on axis while in reality it isn’t. The margin is small but definitely there..
The only way to make sure is to use the text tool on endpoints, which will display it’s coordinates. This only works inside groups and components though..