What does more than mean

More than typically means to add. The symbol that can be used is "+".

Less than means to subtract. With the symbol "-"

For example, 10 + 18 = 28. (More than) 

23 + 45 = 68 (More than)

More than is used when you compare different things. Sometimes you will need to use addition or subtraction to solve it.

But more than is for 'addition' although some problems might make you use subtraction to find the answer.

For example:

He got 5 more candies than me.

That means if I got 1 candy, he got 1+5 or 6 candies.

Another example:

He has 400 more points than me:

That means if he had 800 points, then I had 800-400 points or 400 points.

More than can also be used in inequalitied, and for that the sign would be >

Hope that helps :)