5/10 means to divide 10 into 5 like this
  __
10)5

Since 10 won't go into 5, or rather, it goes 0 times,
put a 0 above the 5

   0
10)5


Now put a decimal and a 0
after the 5, like this:

   0  
10)5.0

Now also put a decimal above that decimal, like this:

   0. 
10)5.0

Now think of that 5.0 as if it had no decimal and was 
just 50.  Then 10 divided into 50 gives 5.
So put 5 above the 0.

   0.5
10)5.0

Then when we finish the division by multiplying we
get 50 to go under the 50, leaving room for the decimal:

   0.5
10)5.0
   5 0

And when we subtract we get 0 remainder, so we are done.

   0.5
10)5.0
   5 0
     0

So the answer is 0.5 that we read at the top of the division.

Edwin