How would I put 1/3 into decimals?

Get a ruler in your hands. Measure things until you start to understand how a ruler works. Measure some stuff and figure out where the center is. Say you measure a book and it's 7/8" thick. You look at your ruler and see that every eighth is divided into two sixteenths, so obviously half of 7/8" is going to be 7/16". If you write that out you have 1/2 x 7/8 = 7/16. And you notice that 1/2 is divided into 2/4 and then into 4/8 and so on, so you can convert anything to anything by multiplying all the numbers on top and then all the numbers on bottom.

Other rulers are divided into 10 and 100 parts. But an inch is still an inch, so anything on one ruler can be translated to the other ruler. A half inch on one ruler is 5/10 or 50/100 on the other. An eighth inch is just 12.5 marks when you have 100 marks per inch. A metric ruler divides an inch into 25.4 parts, so a half inch would be 12.7 of those parts. Pretty simple, isn't it? Practice this a bit and people will think you went to wizard school.

One situation is that some numbers can not be divided right. 1/3 is one of them. If you keep dividing, you keep getting more threes. It is 0.33333333 as long as you keep going. 1/7 is another like that. That is 0.1414141414 and on and on. We use dots to indicate that. If we write 0.333... the three dots mean the last three digits repeat.

Now suppose someone gives you a repeating fraction and you want to prove that it is an actual fraction. For instance pi never repeats, so it is not a fraction of any two whole numbers, but 0.12981298.... is. Because it repeats every four digits, we multiply it by 10,000.

10000x = 1298.1298....
x = 0.1298....
------------- SUBTRACT
9999x = 1298

x = 1298/9999 You can punch that into your calculator and see what you get.