Please help me understand what "resolution" I should be using

Thought I'd share this great link on explaining dpi for web vs print.

https://daraskolnick.com/image-dpi-web/

On the web, standard resolution is 96 pixels per inch.  In other words, that's what most browsers are capable of rendering on screen.  

Magazines * web banners vary.  Ask the magazine or ad agency what height, width and dpi they require before you create your images.  Most magazines want at least 150 dpi or higher.

Resolution has to do with print and it depends on what you are printing. Pixel dimension depends on the web size you need.

Maybe this will help:

Understanding resolution |

Resolution is a print parameter.

An image just consists of pixels, discrete sizeless data points. That's all it is, nothing else.

Anything destined for screen viewing - websites, social media and so on - already has a resolution, namely, whatever screen it's viewed on. There already is a pixel grid in the screen, and the image pixels align neatly onto that.

For screen, you'll be asked for certain pixel dimensions. So many pixels high by so many pixels wide. There may be scaling if the website is designed to do so, but it all starts with a pixel size.

On paper, there is no such pixel grid, so one has to be invented. That's the pixels per inch number, aka resolution. There has to be a certain pixel density for an image to look good. A standard requirement for book and magazine print is 300 ppi, but for billboards and wall-sized banners it might be as low as 10 or 15 ppi, because it will be seen from a longer distance. It depends on the use. Ask.

Standard procedure is to do the math. You know the physical size the image is supposed to have, and you know the number of pixels in your file. Do the math, and you know what the ppi number ends up at. If you know how the image will be used, and what a sensible ppi requirement is for that use, you then know what a realistic print size is and if the image is big enough.

(Luckily, you don't have to actually do the math with a calculator, although you can do that. But you can just let Photoshop's Image Size dialog do it for you).