When you skip count you are skipping certain numbers.

For example,  If we want to skip count by twos, it means that we are actually skipping one number in between.
 

Starting at two, we would say  2, 4, 6, 8, 10, 12, 14, 16, 18

Put your finger on the zero, and move two numbers over each time.  This is also a way to skip count by two's.  You are skipping one number in between, but actually you are moving your finger over two times to get to the next number.

Skip counting by fives:

When you are skip counting by fives, you are moving over five numbers, but actually skipping four numbers.

Starting at 5, we would say 5,  10,  15,  20

Skip counting by tens:
Skip counting by ten's,  you are moving over ten  numbers, but actually skipping nine.

Starting at 10, we would say 10,  20,  30,  40