Is it normal for flames to come up through the slots on each side of the bottom of the oven?
Depends on the design of the oven, but yes, this can be normal.  If you mean 'in the oven itself, some flames are visible below the plate at the bottom'.  If you mean 'outside the oven, flames shoot out of the sides', then you should probably avoid using that oven if at all possible.

An old gas oven I had did this.  When the auto-sparker failed, I lit it manually with a fire-lighter using the vents in the base of the oven, and it worked fine.