Resize images for display or get them to show as existing size

So, I have images inserted in a div.thumbnail span. They are pixelating because they are appearing larger than their actual size. I am finding it hard to resize the images to either a controlled size, existing pixel size or otherwise select them. I’m using the template “boot business.” Also, it seems the only way to insert 3 images on a row is to create a table. I don’t see a component option for a CSS columns insert.
BTW, I want to be able to click on the image and drag to resize! That is how DW used to work. I miss this feature.