Images on blog posts

So i have been trying to add images to my blog posts and featured images, however they all come out as weird sizes which makes them blurry/pixelated, too big or too small. Ive been trying out editors online but everytime i make a new sized image it is never correct when i upload to the hueman themed website.

please can someone provide a simple step by step instructions of what i need to do

The page I need help with: [log in to see the link]