Creating HTML Code for meter

I’m somewhat new to all of this, but I want to put a meter or chart on the sidebar of my blog that will calculate or show reductions to the debt I am trying to get rid of. I want something similar to what https://www.singlemomandmoney.blogspot.com has on her blog. I’d like to be able to go into it and adjust it accordingly. Can anyone tell me where I can find a tutorial for this? I’m not sure how to properly google it.