I can explain it. First of all you have to understand that the same unit on the top and on the bottom of a ratio will cancel each other out. For example, if you write " A x Y/A" then the A's will cancel out and you will have only Y.
1. You need a ratio to begin with. A ratio has one metric and one other (imperial) unit in it. Like this for example:
1 kilogram = 2.2 pounds
or
1 yard = 0.91 meters
or anything like that.
This is what you can find in a table of conversion factors.
2. Now you will take your original number that you want to convert and write it down on paper with its unit. It's extremely important to always write down the unit, not just the number. Let's say you've been asked to convert 28 pounds into kilograms, you'd write down:
28 lbs
3. Beside it, pick the conversion ratio from the table that has the unit in it you want to change (in our case, it's pounds) and also has the conversion unit you want to change it into (in our case, kilograms). Write it beside your original number in such a way that "lbs" will cancel "lbs" when you multiply. Like this:
28 lbs x 1 kg/2.2 lbs
If you see what's happening, you have put the unit you want to convert INTO on the top of the multiplication, and the unit you want to cancel out on the bottom. Now having cancelled the two "lbs" out, you will be left with kilograms which is what you wanted to have. Multiply the numbers with a calculator:
28 x 1/2.2 = 12.7
The answer is 12.7 kilograms. You can see that because it's a 1 on top you could have just divided by 28 by 2.2 without having to multiply by 1, and that's how people who are good at it would do it in their head without thinking of the steps.
Doing this, you can convert anything into anything else that you have a ratio for. For example, convert 12.7 kilograms back into pounds? Write your 12.7 kg and then use that same ratio, but write it upside down this time so that kilograms instead of pounds cancels out:
12.7 kg x 2.2 lbs/1 kg = 28 lbs
I hope that helps! You can convert anything just by doing that!