Can someone explain to me how to use a proportional scale please. Thank you

What are you using to draw proportion? I was taught to use a pencil. Hold up your pencil at arms length out in front of you and start with one part of the object. Figure out how long that part of the object is in comparison to the rest of the object. If the portion of the object is 1/3 or 1/6 in comparison, you know that however big you draw your object, that portion needs to be 1/3 or 1/6 of the overall size. Does this help? You can find this information in basic drawing books from the library. I can also scan and attach a picture if you are interested.

Also using pencil but head as measurement. Hold pencil at arms lenth, put finger where head endd,one end at top of head. Put finger where head ends.

Put erase at chin ( bottom of head you just measured) and finger down and you have the length of the torso.

And so on. If using a still life, use same idea but one object against another