size of images

Grettings Everyone,

I am a beginner at web building. I don’t even know if I will be building my site or have a professional web designer build it for me.

My question is concerning image sizes. If I want to put A LOT of images on one page what is the idea size of each image. I want to be able to enlarge each image too.

I know this seems to be pretty basic and maybe a little idiot-like, but I hope you can look past my ignorance.

Thank you
Warmly
Sassafras